fix a bug about json and xml

@@ -272,14 +272,16 @@ Helper function for serving Json, sets content type to application/json:
 ```go
 func (this *AddController) Get() {
     mystruct := { ... }
-    routes.ServeJson(w, &mystruct)
+	this.Data["json"] = &mystruct
+    this.ServeJson()
 }
 ```
 Helper function for serving Xml, sets content type to application/xml:
 ```go
 func (this *AddController) Get() {
     mystruct := { ... }
-    routes.ServeXml(w, &mystruct)
+	this.Data["xml"]=&mystruct
+    this.ServeXml()
 }
 ```
 

@@ -127,7 +127,7 @@ func (c *Controller) Redirect(url string, code int) {
 }
 
 func (c *Controller) ServeJson() {
-	content, err := json.MarshalIndent(c.Data, "", "  ")
+	content, err := json.MarshalIndent(c.Data["json"], "", "  ")
 	if err != nil {
 		http.Error(c.Ctx.ResponseWriter, err.Error(), http.StatusInternalServerError)
 		return
@@ -138,7 +138,7 @@ func (c *Controller) ServeJson() {
 }
 
 func (c *Controller) ServeXml() {
-	content, err := xml.Marshal(c.Data)
+	content, err := xml.Marshal(c.Data["xml"])
 	if err != nil {
 		http.Error(c.Ctx.ResponseWriter, err.Error(), http.StatusInternalServerError)
 		return