Asteroids, part 4

I've been creating increasingly complicated code to handle timed game events and multiple event loops. This has prompted me to look at Pygame Extended, which has a few nice classes (Director, Reactor, Ticker, Scene) to handle these sorts of things. Unfortunately, the author has tied them in to the OpenGL portions of the library as well, making it hard to reuse. I think I'm going to extract the portions I need (or at least the ideas) for my own game.