code: public void add(Metrics m) {
          timeCount += m.timeCount;
          readingTimeCount += m.readingTimeCount;
          nodes += m.nodes;
          backtracks += m.backtracks;
          fails += m.fails;
          restarts += m.restarts;
      }
docs: Add metrics.
  All the metrics are aggregated to the current instance
  
  @param m the metrics to add