Added missing header for OS X

This breaks ABI so that the structure is packed cleaner. Might as well
take these breaks while we can get away with it.

Update reader.md

typo

Added support for a NULL realloc function to bson_writer.

Use __typeof__ instead of typeof

Fixes valgrind back to zero.

Win32 support + BCON

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).

adding the ability to append a bson_iter_t.  Makes it easy to pass
through portions of another bson object without knowing the type.

bcon_extract family of functions that operate like bson_append, but
allowing for extraction and verification of bson, rather than creation.

Also added a bunch of compile time type checking that makes everything a
lot more reasonable.

a varargs bcon_append with a ton of tasty magic.  bcon_append methods
offer declarative bson appending, including nesting, via tokenizing of a
varargs parameter stream.  Some limited macro support to make everything
a little less fragile.

Base functionality relies only on c89 stdarg.h.  Macro support is a
little more limited, but should still be available on any reasonably new
compiler (msvc 2005 and gcc > 3).  The base functions are usable without
their macro wrappers.

The latter does not work in ISO C mode: http://gcc.gnu.org/onlinedocs/gcc/Typeof.html

_bson_grow errors were being ignore by _bson_append_va. Modified _bson_append_va to propogate _bson_grow errors

Fix missing header and pedantic warnings

This saves a bunch of space for bson_iter_t, but does break ABI. But that
should be fine for now. This makes it a lot easier for languages to wrap
the bson_iter_t struct.

strlen(literal) compiles out on GCC and Clang, so by using these macros
you save some typing and cleanliness and get a bit of a speed improvement
over passing -1 for length.