v0.663 - Stacked Orbs in the Proximity

- Orbs now: 4x score, 4x damage and increased movement speed
- Orb bonuses now Stack
- Proximity mines updated with new sound cues
- Press '3' to throw down Proximity Mines (no animations yet)
- Training Gauntlet updated with more tutorial content
- all missions now have overlay maps (Squirrel Town is a little off target but working on a fix)
- Invert Mouse option added to Options -> Controls