Server-forced nickname on connect is not detected

Some servers force a specific nickname on your client as you connect - regardless of what you ask for. In such cases, exirc does not send certain events correctly.

For example, if we use `Client.logon` and ask for the nickname `example`, but the server gives us another nickname, the `{:joined, channel}` message is not sent when joining channels because exirc thinks our nick is `example` when it's actually something different.

This type of "forced nickname" can be detected from the RPL_YOURHOST / 002 message or some of the other "greeting" type messages that arrive when connecting, since those messages contain your actual nickname at that point.

I wonder if this is something exirc should support? I don't know whether this behavior is fully spec-compliant, so not sure if it's something that should be handled by this library. In case it's useful, this is happening with Twitch's IRC server which is already not entirely compliant from what I can tell.