feat!: vigor mortensen

feat!: vigor mortensen

This introduces the new vigor system which replaces the previous armour
point system.

The new Vigor system introduces a new stat based on constitution that
comprises your "vigor". At 100% vigor your defence + damage are at their
highest possible base values. As you fight your vigor drops (until you
visit a healer). As it drops it starts affecting your defence + damage
negatively.

Armour Points still exist, but have been converted into a "durability"
system which goes down much slower per fight and a bit more drastically
if you die. However, nowhere near the same rate as before.

As such, mitigation no longer has any effect.