Revamp Game.TakeScreenShot

This addresses the side-effect of #358 (which should probably be renamed when this is merged).

Instead of doing random stuff like writing out targas and `memcpy`ing all the things, we now use `plCaptureRender` to take our screenshot (at any res DX supports). We also write out PNGs because no one uses TGA anymore... For free, you get aspect ratio "fixes" in `plCaptureRender` and some includes-reorganization...