Add serverside script functions for determining the killers of both players and actors.
Use unsigned ints for script functions returning an object or actor's refNumIndex or mpNum.
Remove updateDeadState() from LocalPlayer and make its code part of updateStatsDynamic() for simplicity.
ActorDeath packets are sent for dead actors before their StatsDynamic packets. They contain the actor's deathReason in a manner similar to that of PlayerDeath packets.
A future commit will replace the deathReason with a variable named killer which will be an mwmp::Target.
