Adds leather/fur tanning.

No longer will butchering animals produce pre-tanned leather or fur; with this PR the harvested skins become perishable (and edible, if you're into that sort of thing) items that must be cured (which prevents decay) via a recipe, then tanned by way of another. Once the second recipe is complete the tanning process begins, it takes about two days before the tanning skins are finished and ready to be unrolled and cut up or otherwise used. All basic recipes required for this process are auto-learn.

Adds a new book which contains recipes (also available a few in existing books) for a more modern (and more efficient) recipe for tanning.

Integrates new items into existing recipes.

Also adds the ability to cut up items made of fur, which had gone MIA recently.
Bonus category fix!