Adding assets for RPG

- Sprited Ammo type in its own sub-file (rocket)
- SpritedFunctional projectile in its own sub-file (rocket)
- Sprited RPG, no in-hand sprite

Still needs an actual RPG to use all of this, but since this seems
decent I'll release this for starters
Experimental RPG added

- Mostly functional, still a fair bit of oddities
Merge pull request #1197 from dylanstrategie/Rocket

Adding assets for RPG