Moved DLangSpec files into their own subdirectory.

This is to help with my future efforts in allowing compilation to EPUB. I have also updated the win32.mak and posix.mak files to accommodate these changes. I've done some simple testing with the posix.mak file but almost none on the win32.mak file. I can't think how I've broken anything (unless, of course, win32 make is substantially different than *nix make).