Alpha Version 0.3

- Changed bullet and enemyBullet sprites so only 1 bullet is needed for
each.
- Removed memory leak for bullets and enemyBullets group.
- Attempted third AI script, issues with changing variables within for
loops has resulted in this being delayed. Possible change of enemy
movement to reduce complexity of script.

Notes:
- Leak still remains with enemies however as spawning is far less
frequent, time taken for leak to become an issue is negligible.

Future Work:
- Add win and failure conditions
- Add score and score update
- Add obstacles
- Add power ups and upgrades if time permits