docs: function a11yPromise (url, viewportSize, verbose) {
      var deferred = Q.defer();
      a11y(url, {viewportSize: viewportSize}, function (err, reports) {
        if (err) {
          deferred.reject(new Error(err));
        } else {
          deferred.resolve({url: url, reports: reports, verbose: verbose});
        }
      });
      return deferred.promise;
    }