Support MESSAGE_REACTION_REMOVE_ALL event.

discord/state.py

@@ -274,6 +274,13 @@ class ConnectionState:
 
             self.dispatch('reaction_add', reaction, member)
 
+    def parse_message_reaction_remove_all(self, data):
+        message =  self._get_message(data['message_id'])
+        if message is not None:
+            old_reactions = message.reactions.copy()
+            message.reactions.clear()
+            self.dispatch('reaction_clear', message, old_reactions)
+
     def parse_message_reaction_remove(self, data):
         message = self._get_message(data['message_id'])
         if message is not None:

docs/api.rst

@@ -233,6 +233,15 @@ to handle it, which defaults to print a traceback and ignore the exception.
     :param reaction: A :class:`Reaction` showing the current state of the reaction.
     :param user: A :class:`User` or :class:`Member` of the user who removed the reaction.
 
+.. function:: on_reaction_clear(message, reactions)
+
+    Called when a message has all its reactions removed from it. Similar to on_message_edit,
+    if the message is not found in the :attr:`Client.messages` cache, then this event
+    will not be called.
+
+    :param message: The :class:`Message` that had its reactions cleared.
+    :param reactions: A list of :class:`Reaction`\s that were removed.
+
 .. function:: on_channel_delete(channel)
               on_channel_create(channel)