TINYGL: Added external interface for tglBlendFunc
TINYGL: Encapsulated pixel access in FrameBuffer class, provided an implementation of glBlendFunc.
TINYGL: Implemented alpha interpolation in triangle rasterization routine.
TINYGL: Implemented alpha blending and color transformation in sprite blitting for Grim TinyGL renderer.
TINYGL: Modified changelog.
Merge pull request #937 from subr3v/glBlend-implementation

TINYGL: glBlendFunc Implementation