Adds stone bow (bullet-shooting crossbow) item and recipe.

Good for small game, easier to make than the normal crossbow, and
slightly smaller.

http://en.wikipedia.org/wiki/Bullet-shooting_crossbow
Tweak.

Some folks might get confused and think 'bullets' in this case refers to
firearm cartridges.
Merge pull request #7921 from Rivet-the-Zombie/bullet-crossbow

Adds stone bow (stone-shooting crossbow) item and recipe.