* data format where series[i] = [x,y,{extras}].
* @param {!number} rollPeriod The number of points over which to average the data
* @param {!DygraphOptions} options The dygraph options.
- * TODO(danvk): be more specific than "Array" here.
* @return {!Array.<[!number,?number,?]>} the rolled series.
*/
handler.prototype.rollingAverage = function(series, rollPeriod, options) {