I've just tagged Libbson 0.2.2 for general release.
It contains a few bug fixes and various performance improvements. In particular, the allocation hot-path of bson_t is now a bit faster.
Additionally, we have a rudimentary ABI check script in the tree to help us prevent ABI breaks. That said, 0.2.2 does include a small API and ABI break for bson_reader_t to make it an opaque structure. This should also help us avoid ABI breaks in the future.
Enjoy Libbson 0.2.2!