c.JSON performance improvement

benchmark                 old ns/op     new ns/op     delta
BenchmarkOneRouteJSON     1143          1053          -7.87%

benchmark                 old allocs     new allocs     delta
BenchmarkOneRouteJSON     4              3              -25.00%

benchmark                 old bytes     new bytes     delta
BenchmarkOneRouteJSON     72            56            -22.22%

render/json.go

@@ -22,8 +22,7 @@ type (
 var jsonContentType = []string{"application/json; charset=utf-8"}
 
 func (r JSON) Render(w http.ResponseWriter) error {
-	w.Header()["Content-Type"] = jsonContentType
-	return json.NewEncoder(w).Encode(r.Data)
+	return WriteJSON(w, r.Data)
 }
 
 func (r IndentedJSON) Render(w http.ResponseWriter) error {
@@ -35,3 +34,8 @@ func (r IndentedJSON) Render(w http.ResponseWriter) error {
 	w.Write(jsonBytes)
 	return nil
 }
+
+func WriteJSON(w http.ResponseWriter, obj interface{}) error {
+	w.Header()["Content-Type"] = jsonContentType
+	return json.NewEncoder(w).Encode(obj)
+}