Add a configurable light level number to player or mob based on items held in either hand

The same way that armor makes you more visible when worn

A torch or any arbitrary item held will add to your visibility

Related: #75

I'd like to support moving lights at some point, but when I do, I want to do it correctly (altering server-side block light levels) and efficiently if possible, which will probably be somewhat involved. This one is on hold for now.

Going to use the other topic as the main thread for all dynamic light-related conversation (linked above; give it a check for updates)