message: Add ImmutableMap#setMany
diff: @@ -27,6 +27,14 @@ export default class ImmutableMap<K, V> {
  this._data = this._data.set(key, value);
  }
  + setMany(entries: [K, V][]): void {
  + let data = this._data.beginMutation();
  + entries.forEach(entry => {
  + data.set(entry[0], entry[1]);
  + });
  + this._data = data.endMutation();
  + }
  +
  remove(key: K): void {
  this._data = this._data.remove(key);
  }
  