TINYGL: Dirty rects system.

This PR contains an implementation of dirty rects system.
You can find more information behind the design and implementation in the following blog posts: 
http://subr3v.blogspot.co.uk/

Wouldn't it be possible to signal back to the rendering-system that "we need more memory", effectively saying "draw everything this frame, reallocate a buffer of twice the size, and start doing dirty rects again next frame"?