STK Cat Mod {Now with 100% more git repos!}

What I've changed in the mod:

- You can have different default powerups (so, not POWERUP_NOTHING anymore),
  and the default powerup is now the zipper.

- You always have nitro.

- Using nitro gives you nitro, instead of taking it away (can help beating
  nitro collecting levels).

- There is no more auto rescue, use backspace instead.

- The speed limit is practically removed (set to the highest float possible)