Add AttachmentWithReplies method for sending attachment together with replies. (#27)

* add json omitempty on button Title field

Share Button only allows the Type field to be presented in the serialized data. Otherwise, you got facebook error:

"Facebook error : (#100) Param [elements][0][buttons][0][title] must be a non-empty UTF-8 encoded string"

* add attachement to senddata

* changes after pull request reviews

messenger.go

@@ -330,6 +330,15 @@ func (m *Messenger) Send(to Recipient, message string) error {
 	return m.SendWithReplies(to, message, nil)
 }
 
+// SendGeneralMessage will send the GenericTemplate message
+func (m *Messenger) SendGeneralMessage(to Recipient, elements *[]StructuredMessageElement) error {
+	r := &Response{
+		token: m.token,
+		to:    to,
+	}
+	return r.GenericTemplate(elements)
+}
+
 // SendWithReplies sends a textual message to a user, but gives them the option of numerous quick response options.
 func (m *Messenger) SendWithReplies(to Recipient, message string, replies []QuickReply) error {
 	response := &Response{

response.go

@@ -72,6 +72,38 @@ func (r *Response) TextWithReplies(message string, replies []QuickReply) error {
 		Recipient: r.to,
 		Message: MessageData{
 			Text:         message,
+			Attachment:   nil,
+			QuickReplies: replies,
+		},
+	}
+
+	data, err := json.Marshal(m)
+	if err != nil {
+		return err
+	}
+
+	req, err := http.NewRequest("POST", SendMessageURL, bytes.NewBuffer(data))
+	if err != nil {
+		return err
+	}
+
+	req.Header.Set("Content-Type", "application/json")
+	req.URL.RawQuery = "access_token=" + r.token
+
+	client := &http.Client{}
+
+	resp, err := client.Do(req)
+	defer resp.Body.Close()
+
+	return err
+}
+
+// AttachmentWithReplies sends a attachment message with some replies
+func (r *Response) AttachmentWithReplies(attachment *StructuredMessageAttachment, replies []QuickReply) error {
+	m := SendMessage{
+		Recipient: r.to,
+		Message: MessageData{
+			Attachment:   attachment,
 			QuickReplies: replies,
 		},
 	}
@@ -299,10 +331,11 @@ type SendMessage struct {
 	Message   MessageData `json:"message"`
 }
 
-// MessageData is a text message with optional replies to be sent.
+// MessageData is a message consisting of text or an attachment, with an additional selection of optional quick replies.
 type MessageData struct {
-	Text         string       `json:"text,omitempty"`
-	QuickReplies []QuickReply `json:"quick_replies,omitempty"`
+	Text         string                       `json:"text,omitempty"`
+	Attachment   *StructuredMessageAttachment `json:"attachment,omitempty"`
+	QuickReplies []QuickReply                 `json:"quick_replies,omitempty"`
 }
 
 // SendStructuredMessage is a structured message template.