Asteroid

Place the asteroid with random angle, and outside of view.
MovementType

Add a MovementType interface which controls the movement of enemies (or
perhaps other space objects) along with a few useful implementations.
Spacescape

Asteroids are created moving towards the centre of the ship (Beeline).
Create a new asteroid every 5 seconds.

(Known: If the delta is large, it doesn’t extrapolate the locations…)
DrawShield

The drawShields will now bounce Asteroids off them and destroy
themselves when they get used up.

Would be nice if we could make the asteroids fade out : )
Also need to do maths to calculate bounce angle, and need some way of
keeping the speed the same.