message: Make DicePool.MODIFIERS extendable
diff: @@ -76,7 +76,7 @@ declare class DicePool<O = any> {
  k: 'keep';
  kh: 'keep';
  kl: 'keep';
  - };
  + } & Partial<Record<string, string | ((this: DicePool, modifier: string) => unknown)>>;
  /* -------------------------------------------- */
  