Added small and large quivers. [CR]

Add two sizes of quivers, plus spawn rules and recipes to craft them. Intended for survivalist types as some simple small-storage wearables. But in a future PR I might try making them actually hold arrows, and either a) require you to have a loaded quiver to fire a bow, or b) let you fire a bow faster with a loaded quiver. (Those are issues for a future PR, however)

I went off the logic of "10 arrows = 1 unit of volume" for determining sizes.

Small quiver only holds 2 volume, but has no COVERS flag, so it won't encumber you.

Large quiver holds 8 volume, still has 0 encumberance but does have a COVERS flag for the torso, so it'll add to cumulative encumberance.