* Keep track of what windows have requested redraw
Instead of using request_animation_frame and sending redraw request
events, just keep track of all windows that have asked for a redraw.
This doesn't handle dispatching the events
* Issue redraw events to windows that request it
* Cargo fmt
* Stop appending canvas to document in web platform
* Remove `tabindex` TODO in web backend
* Return `OsError` instead of panicking on web canvas creation
