TODO :
- correct http://www.cpcwiki.eu/index.php/Creating_images_for_the_Amstrad
- add http://www.mapeditor.org/
- https://code.google.com/p/retrodev/ or new code adapted for z88dk , ( see http://www.libpng.org/pub/png/book/toc.html )
perharps possible to load directly no compressed ( deflate ) png ( removing header ?)