Stars!

Added stars to the game background
- Loaded on a canvas 4 times as big as the screen
- Uses a quad to make it 4 times bigger than (repeats)
- Uses % to have the background follow the ship
- Each star has a slightly different controlled-random color

Todo:
- More vibrant star color possibilities (that still look good)
- Decide between smooth or rough point-styled stars
- Move canvas creation to game:enter(), and create a new canvas each
time a different system is loaded

- It should be pretty efficient because of the canvas/quad, but if you
think there's a way to make it more efficient tell me