- Changed canvas coordinate system to match UI coord system (origin at top left, y axis down)
- Changed mouse coordinate system to match UI and canvas
- No need to pass width/height to ui_begin_frame() anymore
- Clear final surface to clear color, and enable blending layers onto it
- Fixed Batching bug where we were writing to vertex/shape buffers while the previous batch is using them
- Fixed bug where uvTransform uses transform of next shape instead of that of shape being finalized