Remove unused variables to avoid compiler warning
Many minor changes to better support modular renderers.

This uses a tr_config.h based setup so you can easily reuse any renderer
files without worrying about whether the original files point to the old
or new *.h files.

Also removed all of the unchanged files from the OA renderer so it is
easier to view and maintain.
Update README
Sync version
Added build instructions
Sync with code/renderer changes
Make cl_yawspeed and cl_pitchspeed CVAR_CHEAT instead of CVAR_ROM