[WIP] Remove the item limit

This isn't finished, but I'm testing individual parts as I go so this could be pulled anytime someone wants to take a look at it and either merge what's in or give feedback.

I'm touching up things as I see them, so there's a few bug fixes so far (first aid when wielding, reading when dumb, wincurse when FONTDATA is missing).

This PR will roughly look like this:
1) Add support for using position in inventory & player, and the ability to move between position&invlet (done).  Position is the index into the player's inventory if positive, -1 for weapons, and -2 or lower for worn items (-2-worn[index]).
2) Make inventory uis return position (done) and allow selecting items without an invlet (not started)
3) Move users of inventory to use position instead of invlet. (in progress)
4) Remove existing item-limit checks, but add new checks that expect/assign invlets on wielded/worn items and add the ability to clear an assigned invlet w/ spacebar (not started).