0.4.0

We’re on Sprint 4 now, so we can change our version number…

- Moved Test Enemy.prefab to Assets/Prefabs/Enemies
- Projectile.damage is now a public property of Projectile called
Projectile.Damage, not exposed to the Unity Editor. Instead, base
weapon damage will be an exposed public field in each weapon.
Projectile weapons and projectile-firing enemies will assign the base
damage to the projectile on fire. This is for future balance tweaking
purposes.
- Missile force is now also a field on projectile weapons.
- On collision with an enemy, missiles apply a force in the direction
of their velocity based on the product of their momentum (velocity *
mass) and their damage.
- Enemy health and physics interactions now work with Newton and
Heisenberg. Knockback distance field on enemies removed.