message: add callback function
diff: +import { Town } from '../town/_common'
  import { BackgroundName } from './backgroundTraits'
  import { ClassName } from './classTraits'
  import { RaceName, GenderName, AgeName } from './raceTraits'
  @@ -42,6 +43,7 @@ export interface NPC {
  partnerID?: string
  relationships: Record<string, string>
  lifeEvents: string[]
  + callbackFunction?(town: Town): any
  wealth: number
  finances: {
  creditors: Record<string, number>
  