Support for pinned system messages.

discord/enums.py

@@ -42,6 +42,7 @@ class MessageType(Enum):
     call                = 3
     channel_name_change = 4
     channel_icon_change = 5
+    pins_add            = 6
 
 class ServerRegion(Enum):
     us_west       = 'us-west'

discord/message.py

@@ -295,6 +295,9 @@ class Message:
         if self.type is MessageType.default:
             return self.content
 
+        if self.type is MessageType.pins_add:
+            return '{0.name} pinned a message to this channel.'.format(self.author)
+
         if self.type is MessageType.recipient_add:
             return '{0.name} added {1.name} to the group.'.format(self.author, self.mentions[0])
 
@@ -307,6 +310,7 @@ class Message:
         if self.type is MessageType.channel_icon_change:
             return '{0.author.name} changed the channel icon.'.format(self)
 
+        if self.type is MessageType.call:
             # we're at the call message type now, which is a bit more complicated.
             # we can make the assumption that Message.channel is a PrivateChannel
             # with the type ChannelType.group or ChannelType.private