[FeatureRequest] [CommandHandler] Custom callback method argument type converter

```cs
this.CommandHandler.RegisterTypeConversion(typeof(AnyPlayer), findPlayerByAnything);
// ...
AnyPlayer findPlayerByAnything(string input) {
   // resolve AnyPlayer from input through DB or whatever
   if (badInputFormat)
   {
     throw new Exception("Can't parse input to AnyPlayer");
   }

   return foundPlayer;
}
```

something like that