AttackCast now uses messaging with Damage structs to apply hits.

This is slower but more flexible since it doesn't rely on hitting
a Fighter object. Also added a basic Rat enemy.
Added ragdoll to Rat death. Required changes to Health.

Health now takes Damage objects instead of amount. This was
necessary in order to pass HitLocation / Attacker into the
lethal damage call.
Resolved merge.

AttackCasts now send Damage instead of Attack info.