Create strongly-typed IDs

[ethanmoffat]

Currently, character/player IDs and npc indexes are ints. It would be nice if they were strongly typed Id objects that represented a legal range of IDs.

public struct CharacterId
{
   int ID { get; }

   public CharacterId(int id)
      : this()
   {
      if(id <= 0 || id > short.MaxValue)
         throw new ArgumentException($"ID must be between 1 and {short.MaxValue}");

      ID = id;
   }
}