-Addresses #7158
-removes useless variables heat_protection & cold_protection as these were in 99% of circumstances the exact same as body_parts_covered
-added a new variable, heat_conductivity to all items, determining how fast they conduct heat away from you
-added new procs to humans, sweat() & burn_calories() - Now whenever you use up nutriment, you generate heat, but can also expend nutriment to decrease heat.
-refactored how heat transfer away from humans worked
-added mild hypothermia
-added moderate hypothermia
-added severe hypothermia
-added profound hypothermia
-removed damage from extreme cold
-space is no longer cold to humans (because it isn't, duh.), this does not affect atmos.
-upped pressure damage as space is no longer cold.
-probably a bunch of other stuff:
TODO: Macrowave, balancing of things that use cold to kill.
