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
Merge remote-tracking branch 'lrq3000/updated' from https://github.com/lrq3000/openarena_engine/tree/updated

Conflicts:
	Makefile
	README.md
	code/client/cl_main.c
	code/null/null_glimp.c
	code/renderer/tr_local.h
	code/renderer_oa/qgl.h
	code/renderer_oa/tr_backend.c
	code/renderer_oa/tr_font.c
	code/renderer_oa/tr_image.c
	code/renderer_oa/tr_image_png.c
	code/renderer_oa/tr_local.h
	code/renderer_oa/tr_main.c
	code/renderer_oa/tr_scene.c
	code/renderer_oa/tr_shade.c
	code/renderer_oa/tr_shade_calc.c
	code/renderer_oa/tr_shader.c
	code/renderer_oa/tr_surface.c
	code/renderer_oa/tr_types.h
	code/renderer_oa/tr_world.c
	code/sdl/sdl_glimp.c
	code/sdl/sdl_input.c