more stages!

I added more stages. I also made some other changes:

1. You can now pause the game with "p".
2. Start the stage with "space"
3. Brick overlap test now based on mask rather than rectangle.
4. "Resetting" the ball position deducts a life.
5. Stages now specify the number of lives needed to complete them
including resets.
6. The score no longer goes up indefinitely when you get to the next
stage.