Add the `-w/--websocket` option.

`marvirc join` is able to start a WebSocket server, side-by-side with
the IRC client (thanks to `Hoa\Socket\Connection\Group`). Every message
receive by the WebSocket server is given to the IRC client. Thus:

    $ marvirc join -u Marvirc -c '#hoaproject' -w 127.0.0.1:8889&
    $ echo 'foobar' | hoa websocket:client

And hop, Marvirc is speaking on IRC through WebSocket!