doc: udpate composition section.
doc: add section on JSON.
error: ABI break, make bson_error_t use internal message field.
build: bump.
error: fix warnigns on unused variables.
doc: add errors.
doc: cleanup wording
doc: add bson_reader_t docs.
doc: add writer docs.
build: mark bindings as experimental.
build: bump version for release of 0.2.0.
build: post-release bump.
initialization protection.

Libbson is pretty aggressive about warning the consumer of invalid API
use. However, that means that we short circuit some functions. This is
valid since consumers shipping invalid API use is nothing we can protect
against, but this will at least quiet some static analyzers.
the great mongodb rename of 2013.
build: install docs into ${docdir}.
build: fix some portability issues with pthread.
build: build system improvements, soname versioning, abichecks.

Various build system improvements.

 * Try to use -Bsymbolic to avoid PLT jumps.
 * Detect Windows (define OS_LINUX OS_WINDOWS)
 * Verify basic ABI compliance with abicheck.sh and libbson.symbols.
 * Cleanup bson/Makefile.include.