(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

src/spriteloader/png.hpp

@@ -0,0 +1,18 @@
+/* $Id$ */
+
+/** @file png.hpp */
+
+#ifndef SPRITELOADER_PNG_HPP
+#define SPRITELOADER_PNG_HPP
+
+#include "spriteloader.hpp"
+
+class SpriteLoaderPNG : public SpriteLoader {
+public:
+	/**
+	 * Load a sprite from the disk and return a sprite struct which is the same for all loaders.
+	 */
+	bool LoadSprite(SpriteLoader::Sprite *sprite, const char *filename, uint32 file_pos);
+};
+
+#endif /* SPRITELOADER_PNG_HPP */