softgpu: Add support for 32 bit and 16 bit index texture formats.
softgpu: Move texture function emulation to a helper function.
softgpu: static inline everything.
softgpu: Support RGB565, RGBA5551 and RGBA4444 CLUT formats.
softgpu: Clip primitives when one of their vertices is outside the screen coordinate range (the code really needs a cleanup though).
softgpu: Fix triangle strip rendering.
softgpu: Implement CCW cullmode.