Fixed body temperature (equalization and rounding error). Added a few features.

Body temperature now spreads to body parts correctly.
The player can now warm up (rounding error never let the player warm up fully).
Loss of HP causes loss of body temperature.
Standing in water/sewage causes the body to lose heat faster (player does not get *colder*, just cold faster).

EDIT : blood loss isn't working. I don't know how to cancel pull requests or add a commit tthat fixes it :(