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/

From what I see, this is the ONLY place where blitImages are accessed by index into the array, wouldn't it just be simpler to use a linked list for this (and then use iterators here), to avoid the unneccessarily expensive remove_at-call below here?