(svn r10143) -Add: store the filename of the grfs opened and allow easy access to the name

-Codechange: store the SpriteID in the spritecache too
-Add: add a PNG loader for graphical files
-Documentation: added a document to explain the PNG format

source.list

@@ -307,6 +307,8 @@ blitter/blitter.hpp
 # Sprite loaders
 spriteloader/grf.cpp
 spriteloader/grf.hpp
+spriteloader/png.cpp
+spriteloader/png.hpp
 spriteloader/spriteloader.hpp
 
 # Renderer