Hexen II: Hammer of Thyrion (uHexen2)

TODO:
-------------------------------------

- Add a pak-patch application and a launcher for Mac OS X.
- Port code to SDL2.
- Re-visit the messy mouse grab code and clean it up.
- Clean-up the opengl code, modernize it.
- Proper vsync support for opengl.
- Multisampling support for windows opengl.
- Support for several image formats (jpeg, png, etc)
- Maybe model interpolation stuff?
- Increase several engine limits to allow for larger maps, as
  in Fitzquake and QuakeSpasm engines.
- Software renderer: maybe add 16 bit support (r_pixbytes = 2,
  and even 4 for 32 bit)? The current code is largely missing
  translucency pieces and the d_8to16 and d_8to24 translation
  tables.
- Net: Find some way to workaround the infamous router troubles
- Add sound font support to Timidity.
- ALSA, OSS: Add sequencer support for MIDI playback.
- DOS: Implement MIDI music playback (MPU-401, AdLib/FM synth.)
- utils: qbsp, light and vis: improvements?
- utils, texutils: add more texture tools (pcx2wal, etc.)?
- More unification of hexen2 and hexenworld trees
