code: function executeNext(gremlin, i, callback) {
                  if (stopped) return;
                  if (i >= nb) return callback();
                  executeInSeries([gremlin], [], horde, function() {
                      setTimeout(function() {
                          executeNext(gremlin, ++i, callback);
                      }, config.delay);
                  });
              }
docs: done can also be called by stop()