Make __repr__ slightly more detailed and add a few missing ones.

This includes raw events (which didn't have any) and a few other
types that were missing them. Upon review some more useful fields were
added to the repr output which would be more useful during debugging.

discord/message.py

@@ -78,6 +78,9 @@ class Attachment:
         """:class:`bool`: Whether this attachment contains a spoiler."""
         return self.filename.startswith('SPOILER_')
 
+    def __repr__(self):
+        return '<Attachment id={0.id} filename={0.filename!r} url={0.url!r}>'.format(self)
+
     async def save(self, fp, *, seek_begin=True, use_cached=False):
         """|coro|
 
@@ -263,7 +266,7 @@ class Message:
         self._update(channel, data)
 
     def __repr__(self):
-        return '<Message id={0.id} pinned={0.pinned} author={0.author!r}>'.format(self)
+        return '<Message id={0.id} channel={0.channel!r} type={0.type!r} author={0.author!r}>'.format(self)
 
     def _try_patch(self, data, key, transform=None):
         try: