This is the format for the IRC User Command (see [4.1.3 User Message](http://www.irchelp.org/irchelp/rfc/chapter4.html#c4_1_3))

The three values are `username`, `hostname`, and `servername`, followed by `realname` after the comma.  I decided to hardcode `hostname`, but as the docs say:

> Note that hostname and servername are normally ignored by the IRC server when the USER command comes from a directly connected client

So, I'm open to suggestions here.  We could make it:

```php
$this->sendData(sprintf('USER %s Sismo Sismo :%s', $this->nick, $this->nick));
```
Or make them configurable.  But, it doesn't really matter, in any case, so I think defaulting to `sismo` and `nick` work, and and the end user can subclass this method easily if necessary.