- changed the BSON constant to BSON_CODER and scoped it inside
of a module
- changed the directory layout for all of the BSON related files
- updated the C extension to find the BSON files at their new
directory locations
- updated the C extension to use better/safer macros for accessing
the C API; extension now compiles cleanly under rubinius/rbx
- changed directory layout for BSON related tests
- modified the Rakefile to understand the new layout
