Handle CTCP VERSION messages

[osa1]

I thought the "version" messages sent by freenode-connect are some non-standard thing, but apparently it's a widely supported CTCP message: https://tools.ietf.org/id/draft-oakley-irc-ctcp-01.html#version

We should handle these messages properly according to the RFC.

[osa1]

Here's an example VERSION message:

Msg { pfx: Some(User { nick: "freenode-connect", user: "frigg@freenode/utility-bot/frigg" }), cmd: PRIVMSG { target: User("osa1"), msg: "\u{1}VERSION\u{1}", is_notice: false, is_action: false } }

[osa1]

Just an update: we parse these messages, but do not respond.

[trevarj]

This is really similar to a part of what I had to do for #206.
Tiny should also support the command /VERSION <server|nickname>