windows port of libbson

Compatibility
o Migrated internal int types to bson_intN_t from intN_t.  Had to, no
  stdint on windows (but some types existed.  This is cleaner)
o Added a bunch of casts to quiet warnings
o Replaced functions that aren't available or create warnings on windows
o add a cmake build script under build/win32.  Builds and installs under
  win32
o added bson-compat.h, which wraps up a lot of the windows trivia

Bug fixes
o extensive changes to bcon to accommodate windows (some bugs discovered
  due to differences in the varargs calling convention).