Added Win32 support for symlinks.

I needed to find a dotfile manager that supports Windows (for mingw or cygwin or git or Emacs for instance).  Yours seems nice, I quite like it.  I didn't find any python dotfile managers that supported Windows symlinks.  So I added it to yours.  I tried to avoid any dependencies (other than ctypes, which is included).  It works for me, at least.