* WIP: Invader AI
- Adds debug mode for visualizing bounding boxes
- Adds rectangle and line drawing (for debug mode)
- Invaders move as a close approximation to the original game
- TODO: Demonstrates that the blit function needs to ignore black pixels (or "transparency")
- TODO: The invader movement code is really bad
* clippy and fmt
* Refactor Invader movement
* Support "transparency" in blit function
* Scale player movement to 60 pixels per second, regardless of frame rate.
* Add assertions in blit to prevent drawing out of bounds
* Add bullets, shoot with space
* Add lasers, and improve the bullet animation a little bit
* fmt
