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()
OK, so fungal infections are more likely. I recall their being rather difficult to get (I routinely had to strip and stand around in a Bloom for 15 min to get 'em), but you should make a point of mentioning these changes in future.