Binary-compatible w/ 0.6.0-rc2; includes most fixes from 1.4.0

• This release is binary-compatible with 0.6.0-rc2, but not with 0.7.z, which was a mistaken release. This includes the major bug-fixes and enhancements from that and from 1.4.z.
• 0.8.z releases are based on the v0.8.z branch.
• 0.y.z releases continue to use fairly old compilers. Unlike 1.4+.z, they do not require C++11.
• Binary-compatiblility was checked both by careful diffing and by dynamically loading the new version into test_lib_json compiled against 0.6.0-rc2. The handful of old test-failures relate to our relaxed type-checking and type-conversions, which will not matter for typical use-cases. E.g.

* Detail of ValueTest/isInt test failure:
  src/test_lib_json/main.cpp(167): checkIs( integer_, checks )
  src/test_lib_json/main.cpp(249): check.isDouble_ == value.isDouble()
    Expected: false
    Actual  : true
  src/test_lib_json/main.cpp(251): check.isUInt_ == value.isUInt()
    Expected: false
    Actual  : true

• Of course, current tests all pass.