code: function index(options) {
    const {
      file,
      config,
      logStart,
      logNotFound,
      logEnd,
      defaultContent = defaultFileContent,
    } = options;
  
    logger.log(logStart);
  
    return readConfig(config)
      .then(input => validateExtensions(input))
      .then(input => createStrings(input))
      .then(input => writeExtensionFile({
        input,
        file,
        defaultContent,
        logNotFound,
        logEnd,
      }));
  }
docs: Creates an index.
  @param {Object} options The indexing options,
  @return {Promise}