README: Clean up.

* Consistently use two spaces after a period.  It makes no difference
  to the rendered result but allows text-processing tools to distinguish
  between the period at the end of a sentence and the period at the end
  of an abbreviation within a sentence.
* Re-wrap all paragraphs.
* Use indentation instead of backticks for code blocks.  This makes them
  easier to read in the source.
* Use `inline code markup` where appropriate.
* Add missing punctuation here and there.
* Use proper quotes.
* Fix a typo.
* Remove a sentence that was meant to link to the POSIX spec but didn't
  actually contain a link.  It's a moving target, and I'm sure readers
  know how to find it if they don't already have a copy.

README.md

@@ -14,12 +14,12 @@ matching library with some exciting features such as approximate
 
 The matching algorithm used in TRE uses linear worst-case time in
 the length of the text being searched, and quadratic worst-case
-time in the length of the used regular expression. 
+time in the length of the used regular expression.
 
 In other words, the time complexity of the algorithm is O(M^2N), where
 M is the length of the regular expression and N is the length of the
-text. The used space is also quadratic on the length of the regex, but
-does not depend on the searched string. This quadratic behaviour
+text.  The used space is also quadratic on the length of the regex,
+but does not depend on the searched string.  This quadratic behaviour
 occurs only on pathological cases which are probably very rare in
 practice.
 
@@ -44,35 +44,33 @@ You will need the following tools installed on your system:
 Building
 --------
 
-First, prepare the tre.  Change to the root of the source directory
+First, prepare the tree.  Change to the root of the source directory
 and run
-```
-./utils/autogen.sh
-```
+
+    ./utils/autogen.sh
+
 This will regenerate various things using the prerequisite tools so
 that you end up with a buildable tree.
 
 After this, you can run the configure script and build TRE as usual:
-```
-./configure
-make
-make check
-make install
-```
+
+    ./configure
+    make
+    make check
+    make install
 
 
 Building a source code package
 ------------------------------
 
 In a prepared tree, this command creates a source code tarball:
-```
-./configure && make dist
-```
+
+    ./configure && make dist
 
 Alternatively, you can run
-```
-./utils/build-sources.sh
-```
+
+    ./utils/build-sources.sh
+
 which builds the source code packages and puts them in the `dist`
 subdirectory.  This script needs a working `zip` command.
 
@@ -89,16 +87,16 @@ Approximate matching
 --------------------
 
 Approximate pattern matching allows matches to be approximate, that
-is, allows the matches to be close to the searched pattern under
-some measure of closeness. TRE uses the edit-distance measure (also
-known as the Levenshtein distance) where characters can be
-inserted, deleted, or substituted in the searched text in order to
-get an exact match. 
+is, allows the matches to be close to the searched pattern under some
+measure of closeness.  TRE uses the edit-distance measure (also known
+as the Levenshtein distance) where characters can be inserted,
+deleted, or substituted in the searched text in order to get an exact
+match.
 
 Each insertion, deletion, or substitution adds the distance, or cost,
-of the match. TRE can report the matches which have a cost lower than
-some given threshold value. TRE can also be used to search for matches
-with the lowest cost.
+of the match.  TRE can report the matches which have a cost lower than
+some given threshold value.  TRE can also be used to search for
+matches with the lowest cost.
 
 TRE includes a version of the agrep (approximate grep) command line
 tool for approximate regexp matching in the style of grep. Unlike
@@ -110,19 +108,19 @@ deletion and substitution.
 Strict standard conformance
 ---------------------------
 
-POSIX defines the behaviour of regexp functions precisely. TRE
+POSIX defines the behaviour of regexp functions precisely.  TRE
 attempts to conform to these specifications as strictly as possible.
 TRE always returns the correct matches for subpatterns, for example.
 Very few other implementations do this correctly.  In fact, the only
 other implementations besides TRE that I am aware of (free or not)
 that get it right are Rx by Tom Lord, Regex++ by John Maddock, and the
 AT&T ast regex by Glenn Fowler and Doug McIlroy.
 
-The standard TRE tries to conform to is the IEEE Std 1003.1-2001,
-or Open Group Base Specifications Issue 6, commonly referred to as
-"POSIX".  It can be found online here. The relevant parts are the
-base specifications on regular expressions (and the rationale) and
-the description of the regcomp() API.
+The standard TRE tries to conform to is the IEEE Std 1003.1-2001, or
+Open Group Base Specifications Issue 6, commonly referred to as
+“POSIX”.  The relevant parts are the base specifications on regular
+expressions (and the rationale) and the description of the `regcomp()`
+API.
 
 For an excellent survey on POSIX regexp matchers, see the testregex
 pages by Glenn Fowler of AT&T Labs Research.
@@ -131,58 +129,57 @@ Predictable matching speed
 --------------------------
 
 Because of the matching algorithm used in TRE, the maximum time
-consumed by any regexec() call is always directly proportional to
+consumed by any `regexec()` call is always directly proportional to
 the length of the searched string. There is one exception: if back
 references are used, the matching may take time that grows
-exponentially with the length of the string. This is because
-matching back references is an NP complete problem, and almost
-certainly requires exponential time to match in the worst case.
+exponentially with the length of the string.  This is because matching
+back references is an NP complete problem, and almost certainly
+requires exponential time to match in the worst case.
 
 Predictable and modest memory consumption
 -----------------------------------------
 
-A regexec() call never allocates memory from the heap. TRE
-allocates all the memory it needs during a regcomp() call, and some
-temporary working space from the stack frame for the duration of
-the regexec() call. The amount of temporary space needed is
-constant during matching and does not depend on the searched
-string. For regexps of reasonable size TRE needs less than 50K of
-dynamically allocated memory during the regcomp() call, less than
-20K for the compiled pattern buffer, and less than two kilobytes of
-temporary working space from the stack frame during a regexec()
-call. There is no time/memory tradeoff. TRE is also small in code
-size; statically linking with TRE increases the executable size
-less than 30K (gcc-3.2, x86, GNU/Linux).
+A `regexec()` call never allocates memory from the heap. TRE allocates
+all the memory it needs during a `regcomp()` call, and some temporary
+working space from the stack frame for the duration of the `regexec()`
+call.  The amount of temporary space needed is constant during
+matching and does not depend on the searched string. For regexps of
+reasonable size TRE needs less than 50K of dynamically allocated
+memory during the `regcomp()` call, less than 20K for the compiled
+pattern buffer, and less than two kilobytes of temporary working space
+from the stack frame during a `regexec()` call.  There is no time /
+memory tradeoff. TRE is also small in code size; statically linking
+with TRE increases the executable size less than 30K (gcc-3.2, x86,
+GNU/Linux).
 
 Wide character and multibyte character set support
 --------------------------------------------------
 
-TRE supports multibyte character sets. This makes it possible to
-use regexps seamlessly with, for example, Japanese locales. TRE
-also provides a wide character API.
+TRE supports multibyte character sets.  This makes it possible to use
+regexps seamlessly with, for example, Japanese locales.  TRE also
+provides a wide character API.
 
 Binary pattern and data support
 -------------------------------
 
-TRE provides APIs which allow binary zero characters both in
-regexps and searched strings. The standard API cannot be easily
-used to, for example, search for printable words from binary data
-(although it is possible with some hacking). Searching for patterns
-which contain binary zeroes embedded is not possible at all with
-the standard API.
+TRE provides APIs which allow binary zero characters both in regexps
+and searched strings.  The standard API cannot be easily used to, for
+example, search for printable words from binary data (although it is
+possible with some hacking).  Searching for patterns which contain
+binary zeroes embedded is not possible at all with the standard API.
 
 Completely thread safe
 ----------------------
 
-TRE is completely thread safe. All the exported functions are
+TRE is completely thread safe.  All the exported functions are
 re-entrant, and a single compiled regexp object can be used
-simultaneously in multiple contexts; e.g. in main() and a signal
+simultaneously in multiple contexts; e.g. in `main()` and a signal
 handler, or in many threads of a multithreaded application.
 
 Portable
 --------
 
-TRE is portable across multiple platforms. Here's a table of
+TRE is portable across multiple platforms.  Here's a table of
 platforms and compilers that have been successfully used to compile
 and run TRE:
 
@@ -206,7 +203,7 @@ and run TRE:
 
 TRE 0.7.5 should compile without changes on all of the above
 platforms.  Tell me if you are using TRE on a platform that is not
-listed above, and I'll add it to the list. Also let me know if TRE
+listed above, and I'll add it to the list.  Also let me know if TRE
 does not work on a listed platform.
 
 Depending on the platform, you may need to install libutf8 to get
@@ -215,85 +212,84 @@ wide character and multibyte character set support.
 Free
 ----
 
-TRE is released under a license which is essentially the same as
-the "2 clause" BSD-style license used in NetBSD.  See the file
-LICENSE for details.
+TRE is released under a license which is essentially the same as the
+“2 clause” BSD-style license used in NetBSD.  See the file LICENSE for
+details.
 
 Roadmap
 -------
 
-There are currently two features, both related to collating
-elements, missing from 100% POSIX compliance. These are:
+There are currently two features, both related to collating elements,
+missing from 100% POSIX compliance.  These are:
 
-* Support for collating elements (e.g. [[.\<X>.]], where \<X> is a
-  collating element). It is not possible to support
-  multi-character collating elements portably, since POSIX does
-  not define a way to determine whether a character sequence is a
-  multi-character collating element or not.
+* Support for collating elements (e.g. `[[.\<X>.]]`, where `\<X>` is a
+  collating element).  It is not possible to support multi-character
+  collating elements portably, since POSIX does not define a way to
+  determine whether a character sequence is a multi-character
+  collating element or not.
 
-* Support for equivalence classes, for example [[=\<X>=]], where
-  \<X> is a collating element. An equivalence class matches any
-  character which has the same primary collation weight as
-  \<X>. Again, POSIX provides no portable mechanism for
-  determining the primary collation weight of a collating
-  element.
+* Support for equivalence classes, for example `[[=\<X>=]]`, where
+  `\<X>` is a collating element.  An equivalence class matches any
+  character which has the same primary collation weight as `\<X>`.
+  Again, POSIX provides no portable mechanism for determining the
+  primary collation weight of a collating element.
 
 Note that other portable regexp implementations don't support
-collating elements either. The single exception is Regex++, which
+collating elements either.  The single exception is Regex++, which
 comes with its own database for collating elements for different
-locales. Support for collating elements and equivalence classes has
-not been widely requested and is not very high on the TODO list at
-the moment.
+locales.  Support for collating elements and equivalence classes has
+not been widely requested and is not very high on the TODO list at the
+moment.
 
 These are other features I'm planning to implement real soon now:
 
 * All the missing GNU extensions enabled in GNU regex, such as
-  [[:<:]] and [[:>:]]
+  `[[:<:]]` and `[[:>:]]`.
 
-* A REG_SHORTEST regexec() flag for returning the shortest match
+* A `REG_SHORTEST` `regexec()` flag for returning the shortest match
   instead of the longest match.
 
-* Perl-compatible syntax
-  * `[:^class:]`  
-    Matches anything but the characters in class. Note that
-    `[^[:class:]]` works already, this would be just a
-    convenience shorthand.
+* Perl-compatible syntax:
+  * `[:^class:]`
+    Matches anything but the characters in class.  Note that
+    `[^[:class:]]` works already, this would be just a convenience
+    shorthand.
 
-  * `\A`  
-    Match only at beginning of string
+  * `\A`
+    Match only at beginning of string.
 
-  * `\Z`  
-    Match only at end of string, or before newline at the end
+  * `\Z`
+    Match only at end of string, or before newline at the end.
 
-  * `\z`  
-    Match only at end of string
+  * `\z`
+    Match only at end of string.
 
-  * `\l`  
-    Lowercase next char (think vi)
+  * `\l`
+    Lowercase next char (think vi).
 
-  * `\u`  
-    Uppercase next char (think vi)
+  * `\u`
+    Uppercase next char (think vi).
 
-  * `\L`  
-    Lowercase till \E (think vi)
+  * `\L`
+    Lowercase till `\E` (think vi).
 
-  * `\U`  
-    Uppercase till \E (think vi)
+  * `\U`
+    Uppercase till `\E` (think vi).
 
-  * `(?=pattern)`  
+  * `(?=pattern)`
     Zero-width positive look-ahead assertions.
 
-  * `(?!pattern)`  
+  * `(?!pattern)`
     Zero-width negative look-ahead assertions.
 
-  * `(?<=pattern)`  
+  * `(?<=pattern)`
     Zero-width positive look-behind assertions.
 
   * `(?<!pattern)`
     Zero-width negative look-behind assertions.
 
-Documentation especially for the nonstandard features of TRE, such
-as approximate matching, is a work in progress (with "progress"
-loosely defined...)  If you want to find an extension to use, reading
-the `include/tre/tre.h` header might provide some additional hints if
-you are comfortable with C source code.
+Documentation especially for the nonstandard features of TRE, such as
+approximate matching, is a work in progress (with “progress” loosely
+defined...)  If you want to find an extension to use, reading the
+`include/tre/tre.h` header might provide some additional hints if you
+are comfortable with C source code.