code: function ReadableSerial(list, iterator, callback)
  {
    if (!(this instanceof ReadableSerial))
    {
      return new ReadableSerial(list, iterator, callback);
    }
  
    // turn on object mode
    ReadableSerial.super_.call(this, {objectMode: true});
  
    this._start(serial, list, iterator, callback);
  }
docs: Streaming wrapper to `asynckit.serial`
  
  @param   {array|object} list - array or object (named list) to iterate over
  @param   {function} iterator - iterator to run
  @param   {function} callback - invoked when all elements processed
  @returns {stream.Readable#}