Jelly DLC added

With the jam organizer's permission, the game has been updated to add a third playable character - Jelly - with a new mech that has unique weapon and ability.

Other minor changes:

- Added Space as alternative special ability button, because middle mouse just doesn't work very well with Jelly's ability (you can only hold so many mouse buttons at the same time)

- Made Slimekin voiceclip louder as it could barely be heard before

- Adjusted flamethrower's ammo consumption rate a little bit