libdispatch for Win32

This is libdispatch ported to work on Win32 systems, and lightly tested.

For information see:

http://blog.quiscalusmexicanus.org/post/4906301357/grand-central-dispatch-for-win32-why-i-want-it http://blog.quiscalusmexicanus.org/post/4916668260/grand-central-dispatch-for-win32-the-port http://blog.quiscalusmexicanus.org/post/4919777397/grand-central-dispatch-for-win32-the-source-code http://blog.quiscalusmexicanus.org/post/4929297740/grand-central-dispatch-for-win32-things-still-to-do