Basic health rewrite 1

First chunk of the health rewrite. This PR:
* Reworks the health system. The new system ranges from approximately -100 to 100, and updates on a 6 hour basis. Effects from food stack up a modifier on the next roll, which decreases greatly each time a roll is made, decaying to virtually nothing after the course of a day or so. As a result health is now a much better value of how healthy the player has been in the long term.
* Health now affects how fast the player heals while sleeping, with it being able to provide up to a +/- 1 in 4 chance, (the same as the default heal chance). This means low health players may not heal at all, and high health ones may heal additionally fast. Also performed a slight rework on the healing system while asleep, which now can handle stacking chances for players to heal much better.
* Made AEP_SICK artifacts have an effect again.
* Many things that used to affect health directly now affect your health modifier instead.
* Fixed a few small coding logic errors I stumbled upon.
* Styled Player::mend()
The logic here was flawed. Previously it worked like this:
1) If the player was hibernating and they were not hungry and not thirsty they would heal every 250 turns.
2) If the player was hungry or they were *not* thirsty (due to a flipped sign on the second check) they would then heal every 50 turns, regardless of if they were hibernating or not.

This meant hibernators were healing faster than even normal people were. It also meant that people who were not hungry and thirsty wouldn't heal at all, regardless of how much they slept. Add on top of that that both blocks should *never* trigger together, and it cries out to use an if()/else if() rather then two separate if() blocks.

The new logic works like this:
1) If the person is a hibernator and they are not hungry and not thirsty, they heal every 350 game turns.
2) Else they heal every 50 game turns.

By switching to an if/else if it removes the broken logic, and automatically means that any hibernators who get hungry/thirsty will be automatically bumped up into normal sleep. There's no need to recheck hunger and thirst, since if they are a hibernator that falls to the else if block they will have already implicitly passed the tests that were previously present.