Mobs on Fire system

Needs code review, etc. THIS CURRENTLY HAS NO AFFECT ON SIMPLE MOBS, BUT WILL BE EXPANDED UPON IF PULLED.

New vars for mob/living
on_fire = 0 (Are we on fire?)
fire_stacks = 0 (Measures how flammable/fireintensity you're at, the cap is +-20)

Procs in mob/living
handle_fire() in the life() of mobs (Deals with being on fire)
update_fire() for updating overlays for the mob so we can tell if we're on fire
IgniteMob()
ExtinguishMob()

Modifies fire_act() on most mobs so that it add stacks and ignites instead of simply increasing body temperature

Basics of the system:
Mobs can be lit on fire if they have fire stacks on them. Fire stacks cap out at +-20 max. If you are on fire, and your fire stacks go to 0, you're extinguished. If you go onto a tile without oxygen, you're extinguished. If you get blasted by an extinguisher, you're extinguished. Standing under a running shower will also extinguish you. Mobs can use resist ('cept borgs) to apply Weaken(5) to themselves and remove 5 stacks from themselves. Weaken(5) is the same length as a detective's bullet stun. You do not stop burning unless extinguished.

Fire stacks can go into the negatives by splashing yourself with water, but you slowly dry off back to the baseline of 0. If you are on fire, you will set off plasma fires when entering them. Fire deals damage in the case of Humans and Aliens by increasing your body temperature to the point where handle_environment() damages you. In the case of Monkeys and Borgs, it instead deals direct burn damage, as they don't care about body temperature.

Fire stack sources:
Lasers +5
Heat Ray +20
Splashed by welding fuel +(volume/10)
Splashed by water -(volume/10)
Standing in a hotspot (+5)
Showers (Extinguishes and sets you to -20)

Ignition sources (You can only ignite if you have been given a stack!):
Lasers
Heat Ray
Smoking a cigar/cigarette
Lighters
Welders
Standing in a hotspot (Only ignites at 9+ stacks)