Add projectile shooting

[agnacore]

Ships can shoot projectiles from their bow, and the projectiles move across the screen.

Start with bullets for now.

Some firing rate limit might be good to have? And a limit on the max projectiles on screen.

step 4: set up rudimentary projectile superclass 4.1: spawn a shot 4.2: move that shot 4.3: create a method to shoot it from the ship's front 4.4: ~boom! method (damage? might need to do this after 5)~

[agnacore]

step 4: set up rudimentary projectile superclass 4.1: spawn a shot 4.2: move that shot 4.3: create a method to shoot it from the ship's front 4.4: boom! method (damage? might need to do this after 5)