Add FaceBook parametric codes

docs/readme-facebook.md

@@ -304,6 +304,7 @@ bot.reply(message, reply_message)
 
 Messenger Codes can be scanned in Messenger to instantly link the user to your bot, no typing needed. They're great for sticking on fliers, ads, or anywhere in the real world where you want people to try your bot.
 
+- Get Static Codes :
 ```javascript
 controller.api.messenger_profile.get_messenger_code(2000, function (err, url) {
     if(err) {
@@ -314,6 +315,17 @@ controller.api.messenger_profile.get_messenger_code(2000, function (err, url) {
 });
 ```
 
+- Get Parametric Codes :
+```javascript
+controller.api.messenger_profile.get_messenger_code(2000, function (err, url) {
+    if(err) {
+        // Error
+    } else {
+        // url
+    }
+}, 'billboard-ad');
+```
+
 ## Thread Settings API
 
 Thread settings API is now messenger profile API, it's highly recommended to use profile API instead of thread settings one, however, Botkit thread settings interface still available :

lib/Facebook.js

@@ -544,11 +544,16 @@ function Facebookbot(configuration) {
                     }
                 });
         },
-        get_messenger_code: function(image_size, cb) {
+        get_messenger_code: function(image_size, cb, ref) {
             var message = {
                 'type': 'standard',
                 'image_size': image_size || 1000
             };
+
+            if(ref) {
+                message.data = {'ref': ref};
+            }
+
             request.post('https://graph.facebook.com/v2.6/me/messenger_codes?access_token=' + configuration.access_token,
                 {form: message},
                 function(err, res, body) {