counters.go
func newMultiValueCounter(point Point) accumulatingCounter {
	values := make(map[string]int)
	values[point.Id()] = 1
	return &multiValueAccumulatingCounter{
		newSingleValueAccumulatingCounter(point).(*singleValueAccumulatingCounter),
		values,
	}
}
func newMultiValueCounter(point Point) accumulatingCounter {
	values := make(map[string]int)
	values[point.Id()] = 1
	return &multiValueAccumulatingCounter{
		newSingleValueAccumulatingCounter(point).(*singleValueAccumulatingCounter),
		values,
	}
}
// Multi value counter.