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/

There's an underlying assumption there that you're running on a system with protected memory. AmigaOS 4 does not have that, and even if you have that, there is no real guarantee that an out-of-bounds-access will crash your program at once.