counter.go
func (m *CirconusMetrics) Set(metric string, val uint64) {
	m.cm.Lock()
	defer m.cm.Unlock()
	m.counters[metric] = val
}
func (m *CirconusMetrics) Set(metric string, val uint64) {
	m.cm.Lock()
	defer m.cm.Unlock()
	m.counters[metric] = val
}
// Set a counter to specific value