- Improved heater efficiency a bit and lowered the chance of getting sick when too cold inside the shelter

Sick and heat config
 -- Heat Coefficient 1.25 (1.65) / Heat Curvature 0.75 (unchanged): heater efficiency reduced to 1.6°C per fuel instead of 2.2°C (about 25% less)
 -- Max Sick Probability 0.8 (1): maximum chance of getting sick changed from 100% to 80%

//Formula is (Heat Coefficient) / (Heat Curvature) = (Heat generated by each fuel)
By default, a basic heater generates +2.2°C per fuel (1.65 / 0.75), and the maximum heat generated is 2.2 x 6 = +13°C (can have up to 6 fuel in one heater). With this mod, it's reduced to only +10°C.