Add cog_load and cog_unload method (#34)

* Add `cog_load` and `cog_unload` method

* Move `cog_load` to end

* Resolve conflict

docs/ext/commands/api.rst

@@ -19,6 +19,11 @@ Command
 .. autoclass:: revolt.ext.commands.Command
     :members:
 
+Cog
+~~~~
+.. autoclass:: revolt.ext.commands.Cog
+    :members:
+
 command
 ~~~~~~~~
 .. autodecorator:: revolt.ext.commands.command

revolt/ext/commands/cog.py

@@ -32,18 +32,30 @@ class Cog(metaclass=CogMeta):
     _commands: list[Command]
     qualified_name: str
 
-    def _inject(self, client: CommandsClient):
+    def cog_load(self):
+        """A special method that is called when the cog gets loaded."""
+        pass
+
+    def cog_unload(self):
+        """A special method that is called when the cog gets removed."""
+        pass
+
+    def _inject(self, client: CommandsClient):  
         client.cogs[self.qualified_name] = self
 
         for command in self._commands:
             command.cog = self
             client.add_command(command)
 
+        self.cog_load()
+
     def _uninject(self, client: CommandsClient):
         for name, command in client.all_commands.copy().items():
             if command in self._commands:
                 del client.all_commands[name]
 
+        self.cog_unload()
+
     @property
     def commands(self) -> list[Command]:
         return self._commands