add flusher interface and implementation

ron.go

@@ -22,6 +22,7 @@ type (
 
 	responseWriterWrapper struct {
 		http.ResponseWriter
+		http.Flusher
 		headerWritten bool
 	}
 
@@ -76,6 +77,10 @@ func (w *responseWriterWrapper) Write(b []byte) (int, error) {
 	return w.ResponseWriter.Write(b)
 }
 
+func (w *responseWriterWrapper) Flush() {
+	w.ResponseWriter.(http.Flusher).Flush()
+}
+
 func defaultEngine() *Engine {
 	return &Engine{
 		mux:      http.NewServeMux(),