-Delete the TODO file. We have more effective means of tracking what projects need to be done in the future.

git-svn-id: http://odamex.net/svn/root/trunk@4584 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Apply pdk's patch to add PNG screenshot support (bug 136). Big thanks to pdk.
-PNG support requires libpng and zlib. If either are missing at compile-time, Odamex will fall back to BMP screenshots.
-Adds the client cvar cl_pngscreenshots (may be removed in the future) to toggle PNG screenshots. cl_pngscreenshots will always be disabled if libpng is missing at compile-time.

git-svn-id: http://odamex.net/svn/root/trunk@4586 b0bcef46-2027-0410-bd56-ab726e9a1d04