Tilemap

Same as: https://github.com/HaxePunk/HaxePunk/pull/200

Currently, when scale or color are set on a Canvas (or Tilemap), rendering is done with BitmapData.draw using a transformation matrix and tint, instead of the much faster copyPixels. This results in a significant performance hit each frame. With this update, the scaled/colored images will be drawn only once onto intermediate buffers, which will then be drawn to the screen using copyPixels each frame, resulting in much faster rendering.

Also fixes issue with aligning Grid/Tilemap when the screen is scaled.