Custom Command Handling

I'm working with a IRC that has custom [CAP](https://github.com/ircv3/ircv3-specifications/blob/master/extensions/cap-notify-3.2.md) (capabilities), which adds more commands. Is there a good way to handle these messages so they can be handled outside of the ExIrc.Client?

Requesting capabilites:

```
< CAP REQ :twitch.tv/membership
```

Example message from the IRC server

```
%IrcMessage{args: ["#rockerboo", "rockerboo"], cmd: "CLEARCHAT", ctcp: false, host: [], nick: [], server: "tmi.twitch.tv", user: []}
```

https://github.com/justintv/Twitch-API/blob/master/chat/capabilities.md#membership