ATTACKING OVERHAUL FINISHED.
Okay, the attacking overhaul works like so- there's a new system called
'attack rules' which determine what attacks are allowed to do. Attacks
move via a variant of the current Creature movement system, which really
should just become the Entity movement system and would do if I was
bolder. I really should just fucking do that. Also tighten up how
movement works to make diagonals honest. ANYHOW.

Attacks have movement parts, those movement parts do their hitbox
checking for them and return if the attack isn't allowed to touch any of
the things that it is touching after this step. Attacks can now be
'friendly' to given factions, and will ignore them for the purposes of
resolving, but can still be set up to specifically not pass through them
if counter-play is fun. Also, parts are now either Launch or Resolve
parts, and both are variants on the good old AttackPart system. Attacks
receive a list of AttackParts and do the split themselves.