- Player hp_max is 8 now, so most injuries will block
a whole slot each time.
- Player can be reduced to 1 slot, not 2. The 2 slots
was from back in the day when players needed to go
to the surface to heal faster, to help them get up
there. Now the 1 slot is only needed in case the
player is trapped in fire or something.
- Damage effects now don't stop playing just because
the player has reached maximum injury, and healing
is also delayed by continued injury.
Guarantee 2 usable slots no matter how many different
injury effects accumulate.
Filled slots will be shared among different damage types
roughly proportionally.
