TODO:

Lots....

Sort the gun animation out, it need to be nicely double buffered and have a clever rotating sprite.

Fix the shootPlayer code. Stop the odd jumping at the end of the run.

Make a nice way for balls to disappear, popping, vanishing, falling, whatever.

Make more levels.

Make something that moves through levels rather than just exiting.

Make more of the code dynamic (less defines, it'd be nice to be able to scale the game while running).

Nicer graphics.

Menu for control, more things to fiddle with.

Add a mechanism to move through the levels.
