* Move all examples to individual crates
* CI: Add libsdl2
* Use Ubuntu bionic for updated libsdl; 2.0.8
* Clippy
* libudev-dev is a dependency of libsdl2-dev
* Clippy
* Remove unnecessary dev-dependency
* `winit` is actually used in unit tests
* Fix a typo
* Move `simple-invaders` crate
* Implement collision detection
* Minor cleanups.
* Add laser/player collisions
* Add laser collision with bullets and fix fire button repeating
* Add basic shield collisions
* Refactor collision and debug
* Simplify collision and debug by not tracking laser indices
- We don't care about which laser collided, because they get destroyed immediately.
* Don't track laser indicies against bullets either
* DRY and docs
* Adjust the fleet bounding box as invaders are shot
