* Allow unregistration of metrics
* Provide metrics.WritePrometheusSet to write using a dedicated metric set
* Cleanup unregister metrics patch, add generic WriteProcessMetrics
* Add new type of counter: FloatCounter
* sometimes you need to count things with more precision than uint64
* FloatCounter also usefull if you need setable Gauge w/o callback func
* Fix PR review:
* sync.RWMutex -> sync.Mutex
* more idiomatic add/sub