'add to queue' endpoint added (#452)

spotipy/client.py

@@ -1291,6 +1291,30 @@ class Spotify(object):
             )
         )
 
+    def add_to_queue(self, uri, device_id=None):
+        """ Adds a song to the end of a user's queue
+
+            If device A is currently playing music and you try to add to the queue
+            and pass in the id for device B, you will get a
+            'Player command failed: Restriction violated' error
+            I therefore reccomend leaving device_id as None so that the active device is targeted
+
+            :param uri: song uri, id, or url
+            :param device_id:
+                the id of a Spotify device.
+                If None, then the active device is used.
+
+        """
+
+        uri = self._get_uri("track", uri)
+
+        endpoint = "me/player/queue?uri=%s" % uri
+
+        if device_id is not None:
+            endpoint += "&device_id=%s" % device_id
+
+        return self._post(endpoint)
+
     def _append_device_id(self, path, device_id):
         """ Append device ID to API path.