Add ability to configure which renderers are used by love.graphics.

- Add t.renderers and t.excluderenderers love.conf fields. They can be an array of renderer names.
- Add --renderers a,list,of,renderernames and --excluderenderers more,renderers argument options.

src/modules/graphics/opengl/Graphics.cpp

@@ -1599,7 +1599,7 @@ void Graphics::releaseBufferMapMemory(void *mem)
 		free(mem);
 }
 
-Graphics::Renderer Graphics::getRenderer() const
+Renderer Graphics::getRenderer() const
 {
 	return RENDERER_OPENGL;
 }