Butchering results

Change butchering to give items from a list loaded from an item groups file, so that mods can add items to corpses and allow a greater array of options.

Item group alone wouldn’t be enough, because of how skill/tools/stats dictate loss at butchery. It would require something new, like item groups+counts+loss threshold.

Item group could specify a max return, then butchering could roll a percentage of that max?