code: function (options, callback) {
              var query,
                  handler,
                  retry = false,
                  params,
                  args = arguments;
  
              if (typeof options === 'function') {
                  callback = options;
                  params = {};
              } else {
                  params = extend({}, options.params);
                  retry = options.retry;
              }
  
              retry = (retry === true) && function () {
                  this.list.apply(this, args);
              }.bind(this);
  
              if (params['created_before']) {
                  params['created_before'] = getTimestamp(params['created_before']);
              }
  
              if (params['created_after']) {
                  params['created_after'] = getTimestamp(params['created_after']);
              }
  
              query = querystring.stringify(params);
              if (query) {
                  query = '?' + query;
              }
  
              handler = createResponseHandler(callback, retry);
  
              return req(client.documentsURL + query, handler);
          }
docs: Fetch a list of documents uploaded using this API key
  @param   {Object}   [options]                        List options
  @param   {boolean}  [options.retry]                  Whether to retry the request after 'retry-after' seconds if the retry-after header is sent
  @param   {Object}   [options.params]                 URL parameters
  @param   {int}      [options.params.limit]           The number of documents to return (default: 10, max: 50)
  @param   {Date}     [options.params.created_before]  An upper limit on the creation timestamps of documents returned (default: now)
  @param   {Date}     [options.params.created_after]   A lower limit on the creation timestamps of documents returned
  @param   {Function} [callback]                       A callback to call with the response data (or error)
  @returns {Request}