introduce helper function

wechatMsg.go

 	close(m.instantResponse)
 }
 
-func (m *InWechatMsg) immediateResponse(s string) {
-	m.instantResponse <- s
+func (m *InWechatMsg) replyXML(xml string) {
+	m.instantResponse <- xml
+}
+
+func (m *InWechatMsg) replyText(s string) {
+	str, _ := BuildTextMsg(m.header.FromUserName, s)
+	m.instantResponse <- str
 }