Add instrumentation with prometheus

lib/instrument/dummy.go

@@ -0,0 +1,14 @@
+// +build noprometheus
+
+package instrument
+
+import "time"
+
+type dummyInst struct{}
+
+func Init() Instrument {
+	return &dummyInst{}
+}
+
+func (i dummyInst) Visit(section string, id string, search string, fmt string) {}
+func (i dummyInst) Duration(section string, duration time.Duration)            {}