Broadens hat encumbrance

This adds encumbrance and the VARSIZE tag to most hats.  It's intended to discourage wearing multiple hats & helmets over hats.

(It's possible to wear one hat over another IRL--I've done it--but only if the first fits you well and the second is a bit looser.  Bulky headgear should prevent other stuff on top of it.  (Top hat, I'm looking at you.)