[commands] Add on_command and on_command_completion events.

discord/ext/commands/bot.py

@@ -514,7 +514,8 @@ class Bot(GroupMixin, discord.Client):
         --------
         This function is necessary for :meth:`say`, :meth:`whisper`,
         :meth:`type`, :meth:`reply`, and :meth:`upload` to work due to the
-        way they are written.
+        way they are written. It is also required for the :func:`on_command`
+        and :func:`on_command_completion` events.
 
         Parameters
         -----------
@@ -553,8 +554,10 @@ class Bot(GroupMixin, discord.Client):
 
         if invoker in self.commands:
             command = self.commands[invoker]
+            self.dispatch('command', command, ctx)
             ctx.command = command
             yield from command.invoke(ctx)
+            self.dispatch('command_completion', command, ctx)
         else:
             exc = CommandNotFound('Command "{}" is not found'.format(invoker))
             self.dispatch('command_error', exc, ctx)