The WHO command (Modern) and IRCv3 WHOX
TODO: cross-reference RFC 1459 and RFC 2812
When WHO <#chan> is sent, the second parameter of RPL_WHOREPLY must be #chan. See discussion on Modern: <https://github.com/ircdocs/modern-irc/issues/209>
When WHO is sent with a non-existing nickname, the server must reply with a single RPL_ENDOFWHO. See: <https://github.com/ircdocs/modern-irc/pull/216>
https://github.com/ircv3/ircv3-specifications/pull/482