Removed duplicate warp sound, some snd cleanup

Enemy Rocketboots now chases the player when they are close to eachother

Prep for release 0.6.5

Playable Development Snapshot

- Fixed the massive memory leak (by removing SlickUI)
- New main menu and level UI
- Level unlocking functionality complete
- Other bug fixes and improvements

Release 0.4.3 (Christmas 2018)