Rerender frequently via extra ever-present event

This method has a small, but definite, performance impact.
The performance should be evaluated before this gets merged.

Consideration: This could be #ifdef'd for steam, but some people
might run non-steam games via steam and expect the overlay work
well which would be a paint for making it the default, not an ifdef
Continue rerender event after videos
Don't rerender while minimized
Let the REDRAW EVENT take care of resize-redraws

The redraw due to resizing was causing some lag when you resized
quickly because a bunch of render calls/resize events stacked up.
This doesn't occur with the internal event, and it still feels
responsive enough during resizing
Handle HIDDEN/SHOWN window events similarly
Ensure we don't have multiple queued rerender events
Ensure refresh rate doesn't go above screen refresh rate

This should solve the issue on macs where obscuring the
window fully lead to constant rerenders and 100% cpu.
Clear renderer between drawing MPEG frames, fixes #46
Merge pull request #50 from sekaiproject/RenderOverlay

Rerender even while idle for the steam overlay's sake.