Adds survivor utility belt.

A wearable collection of tools with a bonus knife sheath!

Includes item, resource-intensive item recipe, survivor zed item drop, and various code to make it all work.
I hadn't noticed the items' contents to be doubled. The previous system had it so only the contents of worn items would appear in the crafting inventory, but not the worn items themselves.

If I remove p->worn, then a knife in a boot still counts, but not the boot itself. If I were to remove the line after it, would it still count the knife in the boot as well?