[WIP] factor out trace functionality into separate package and add Go docs

daemon/daemon.go

@@ -12,6 +12,7 @@ import (
 
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/zrepl/zrepl/daemon/logging/trace"
 
 	"github.com/zrepl/zrepl/config"
 	"github.com/zrepl/zrepl/daemon/job"
@@ -84,7 +85,7 @@ func Run(ctx context.Context, conf *config.Config) error {
 
 	// register global (=non job-local) metrics
 	zfscmd.RegisterMetrics(prometheus.DefaultRegisterer)
-	logging.RegisterMetrics(prometheus.DefaultRegisterer)
+	trace.RegisterMetrics(prometheus.DefaultRegisterer)
 
 	log.Info("starting daemon")