Add hidpi support on windows and update .gitignore for documentation artifacts

The windows driver now calls SetProcessDPIAware and OpenTK.Examples uses a manifest to enable hidpi mode. This is necessary in order to support hidpi scaling on the new high resolution monitors that have started trickling out. Without it (a) windows scales the OpenTK window (ugly) and (b) the PointToScreen & PointToClient transformations return inconsistent results.

I have also added Documentation/Source to .gitignore, since that directory contains thousands of intermediate doxygen files.

This repo is now rebased on yours, but preserves the complete SVN history, which explains the huge amount of commits.