lib/input-generators/sitemap-index.js
function (options, listener) {
    var opts = Object.assign({}, base.defaults(defaults), options);

    return base.run(opts, generateInput, listener);
  }
function (options, listener) {
    var opts = Object.assign({}, base.defaults(defaults), options);

    return base.run(opts, generateInput, listener);
  }
Generate the input arguments for snapshots from a robots.txt file.
Each input argument generated calls the listener passing the input object.

@param {Object} options - Sitemap index options.
@param {Function} listener - Callback to receive each input.
@returns {Promise} Resolves to undefined on completion.