First-Person Hand Removal

A small mod made on request, this mod does one thing and one thing only: It prevents empty hands from showing up.

Holding a block?  There's a hand.
Using an item?  There's a hand.
Punching wood?  There's a hand.
Standing around holding nothing?  No hand for you!

Source code is publicly available, so feel free to update/backport as you see fit.