Implement CF_DIB support

The clipboard code now supports the `CF_DIB` format on the clipboard. When
found, it takes the data and uses GDI+ to convert it into a JPEG. GDI+ was
used because:

* It's on every Windows machine from XP SP0 onwards (Win2k doesn't work).
* It requires linking to a small gdiplus.lib instead of a massive jpeg
  library.
* It's a really easy interface to use that interops easily with the
  Windows bitmap header information structures.

I think it'd be worth considering this approach for the other screenshot
applications as well, as it'd reduce the jpeg lib dependency and simplify
the codebase.