Unify pixel format enums for ImageData, CompressedImageData, and Canvas into a single PixelFormat enum.

Replace love.graphics.getRawImageFormats and love.graphics.getCompressedImageFormats with love.graphics.getImageFormats.

--HG--
branch : minor

src/modules/graphics/Texture.cpp

@@ -28,7 +28,8 @@ namespace graphics
 Texture::Filter Texture::defaultFilter;
 
 Texture::Texture()
-	: width(0)
+	: format(PIXELFORMAT_UNKNOWN)
+	, width(0)
 	, height(0)
 	, filter(getDefaultFilter())
 	, wrap()
@@ -40,6 +41,11 @@ Texture::~Texture()
 {
 }
 
+PixelFormat Texture::getPixelFormat() const
+{
+	return format;
+}
+
 int Texture::getWidth() const
 {
 	return width;