Added support for DXT1/3/5 and BC5/7 compressed textures via love.image.CompressedData. Some internals are still iffy.

- added a new CompressedData type to love.image
- added love.image.isCompressed(file or data)
- love.graphics.newImage automatically tests for compression when loading a file
- added love.graphics.isSupported strings for DXT, BC5, and BC7

Compressed textures meant to be used on the GPU offer huge performance gains when
- loading the texture from a file
- loading the texture from RAM to VRAM
- loading mipmaps
- rendering

--HG--
branch : image-CompressedData

src/modules/graphics/opengl/Graphics.h

@@ -251,8 +251,8 @@ public:
 	/**
 	 * Creates an Image object with padding and/or optimization.
 	 **/
-	Image *newImage(love::filesystem::File *file);
 	Image *newImage(love::image::ImageData *data);
+	Image *newImage(love::image::CompressedData *cdata);
 
 	/**
 	 * Creates a Quad object.