Merge pull request #22 from hanumantmk/win32

More win32 compat for the mongo c driver
build: bump version to 0.4.3

we've had a bunch of internal changes, so lets go ahead and bump this
again.
bson_from_json support

Support for bson generation from json via yajl

o bson_json_reader_t interface for streaming json parsing
o bson_from_json convenience wrapper
o json-to-bson example program

Supports the full set of strict extended json, at least theoretically