code: function importDirectory(dirPath, options, callback) {
    if (!callback) return _importDirectory(dirPath, options);
    _importDirectory(dirPath, options).then(
      imports=>setImmediate(()=>callback(null, imports)),
      err=>setImmediate(()=>callback(err, undefined))
    );
  }
docs: Import all the modules in a set of given paths,according to the supplied options.
  
  @public
  @param {string|Array.<string>} dirPath   The path(s) to import from.
  @param {Object} [options='']             The option to use in the import.
  @param {Function} [callback]             Node-style callback to fire, use if you do not want a promise.
  @returns {Promise.<Object>}