API renames, change ref renderer to in renderer in IDrawable, make Layer implement IDrawable.

Source/UiLayer.cs

@@ -12,7 +12,7 @@ namespace DaggerFramework
             base.OnUpdate(dt);
             _time += dt;
         }
-        protected override void OnDraw(ref Renderer renderer)
+        protected override void OnDraw(in Renderer renderer)
         {
             renderer.SetTransform(Vector2.Zero);
             renderer.DrawRectangle(new Vector2(720 / 2, 1280), Color.Green);