Desktop Duplication API Grabber

Use the Windows 8 Desktop Duplication API to capture the Desktop on Windows.
Up to 4x FPS compared to WinAPIGrabber, no DWM-stuttering and lower CPU usage.

see http://msdn.microsoft.com/en-us/library/windows/desktop/hh404487%28v=VS.85%29.aspx

I've built with qmake-generated vcxproj's, not tested with msys or other OSes.