Adds different types of Biter/Spitter that resist different types of damage, to encourage varied defences.

Each tier of biter/spitter (only behemoths by default) will gain three resistant variants:
- Physical: +90% resistance
- Laser: +90% resistance
- Fire: 100% resistance
Resistances stack with any existing resistances. For instance, behemoth biters go to 12/91% physical resist (original: 12/10%), whilst small biters go to 0/90% (original: none).

The odds of each variant spawning are, by default:
- Default (no extra resist): 55%
- Each type: 15%
This can be tweaked via the config.

Biters/spitters are also tinted for any active tier:
- Default: White
- Physical: Black
- Laser: Cyan
- Fire: Orange