Shots and collisions

Now that we have a flying saucer to menace the player, both the alien and the player need the ability to fire shots at each other. We will implement two separate types of weapons—one for the player and one for the alien saucer.

The player's shots will travel upward at a constant rate until they either leave the screen or impact the alien saucer. The enemy's shots will act more like bombs, falling under the effect of gravity until they reach the ground.