Add a small prometheus exporter

go.mod

@@ -5,6 +5,9 @@ go 1.12
 require (
 	github.com/go-bindata/go-bindata v3.1.2+incompatible // indirect
 	github.com/gorilla/mux v1.7.3
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.1 // indirect
 	github.com/pkg/errors v0.8.1
+	github.com/prometheus/client_golang v1.1.0
 	go.etcd.io/bbolt v1.3.3
 )