gauge.go
func (m *CirconusMetrics) SetGauge(metric string, val interface{}) {
	m.gm.Lock()
	defer m.gm.Unlock()
	m.gauges[metric] = val
}
func (m *CirconusMetrics) SetGauge(metric string, val interface{}) {
	m.gm.Lock()
	defer m.gm.Unlock()
	m.gauges[metric] = val
}
// SetGauge sets a gauge to a value