Compresspng

It took me some time to understand how to images were encoded, but I got it working. I tested the compression with uSquish on my linux 64 box. The executable file size reduced from 9.4 mb to 9.0 mb. Huge difference! Specially if you imagine this compression on a larger game. 

I am going to add some documentation on the source code (to be done soon) as I follow the project.