function on(type, listener) {
      var object = this,
          events = object.events || (object.events = {});

      _.each(type.split(' '), function(type) {
        (_.has(events, type)
          ? events[type]
          : (events[type] = [])
        ).push(listener);
      });
      return object;
    }
Registers a listener for the specified event type(s).

@memberOf Benchmark, Benchmark.Suite
@param {string} type The event type.
@param {Function} listener The function to register.
@returns {Object} The current instance.
@example

// register a listener for an event type
bench.on('cycle', listener);

// register a listener for multiple event types
bench.on('start cycle', listener);