Quaternion by-product work that needed doing:

- Enemy ships tracking abilities re-implemented, quaternion-style

- Shots re-implemented with quaternions

- Re-worked object struct, getting rid of a lot of unneeded parameters and adding others

Enemies now start off quite weak and non-aggressive, so the early levels are fairly easy

Enemy shields, intelligence and aggressiveness increase with each level

Lots of bug fixes

Did some internal re-naming to make the code more readable