Ship now moves to attack asteroids in range.

Next steps:
     Fix bullets - for some reason the do not all travel to the edge of their range. I think adding a cooldown may fix this issue.
     Fix nullPointerException - occasionally the game crashes with this error. I have not investigated it yet.
     Give the ship a max speed - I've been meaning to do this for a while. I keep getting weird bugs with my method in UserShip class.
     Add a hunt() method in AutonomousShip class - right now the ship will only move in a straight line. This function would make the AI MUCH more impressive.
     Tune the aiming - sometimes the ship just twitches trying to align itself perfectly with an asteroid. Should be easily fixed.