code: function mapLimit (coll, limit, iteratee, callback) {
      return _map(eachOfLimit(limit), coll, iteratee, callback)
  }
docs: The same as [`map`]{@link module:Collections.map} but runs a maximum of `limit` async operations at a time.
  
  @name mapLimit
  @static
  @memberOf module:Collections
  @method
  @see [async.map]{@link module:Collections.map}
  @category Collection
  @param {Array|Iterable|AsyncIterable|Object} coll - A collection to iterate over.
  @param {number} limit - The maximum number of async operations at a time.
  @param {AsyncFunction} iteratee - An async function to apply to each item in
  `coll`.
  The iteratee should complete with the transformed item.
  Invoked with (item, callback).
  @param {Function} [callback] - A callback which is called when all `iteratee`
  functions have finished, or an error occurs. Results is an array of the
  transformed items from the `coll`. Invoked with (err, results).
  @returns {Promise} a promise, if no callback is passed