stop calling validate() in newReader/Writer()

By not calling validate(), we can add
non-invasive features which will be simply ignored when user-code
is compiled against an old version. That way, we can often
avoid a minor version-bump.

The user can call validate() himself if he prefers that behavior.

src/lib_json/json_reader.cpp

@@ -1863,9 +1863,6 @@ CharReaderBuilder::~CharReaderBuilder()
 {}
 CharReader* CharReaderBuilder::newCharReader() const
 {
-  if (!validate(NULL)) throw std::runtime_error("invalid settings");
-  // TODO: Maybe serialize the invalid settings into the exception.
-
   bool collectComments = settings_["collectComments"].asBool();
   OurFeatures features = OurFeatures::all();
   features.allowComments_ = settings_["allowComments"].asBool();

src/lib_json/json_writer.cpp

@@ -968,9 +968,6 @@ StreamWriterBuilder::~StreamWriterBuilder()
 {}
 StreamWriter* StreamWriterBuilder::newStreamWriter() const
 {
-  if (!validate(NULL)) throw std::runtime_error("invalid settings");
-  // TODO: Maybe serialize the invalid settings into the exception.
-
   std::string indentation = settings_["indentation"].asString();
   std::string cs_str = settings_["commentStyle"].asString();
   bool eyc = settings_["enableYAMLCompatibility"].asBool();