Support IRCv3 extensions

[jorgenschaefer]

There's a list of possible extensions for IRC to support:

http://ircv3.net/irc/3.2.html

Check which of those are supported by Freenode (possibly ZNC) and implement them.

[jamienicol]

From the point of view of a ZNC user, I think echo-message and server-time would be the most useful.

[jorgenschaefer]

Good to know, thank you!

[ChrisBuchholz]

Any news on this?

[Thaodan]

IRCv3 priv-message/echo-message would be a blessing on multi client connections.
Without it any message send by the user is not shown in circe when send from another client like communi on a phone.

Priv-message/echo-message is probably the easiest requiring circe to ignore the message being repeated when circe has send the message in a query and before that signifying that circe supports priv-message/echo-message.

So circe has to do this:

1. showing that capability priv-message/echo-message is supported.
2. Message was send by user from different client: do nothing.
3. Message was send by user from circe: don't show repeated message shown by priv-message/echo-message.

See:
https://ircv3.net/specs/extensions/echo-message-3.2.html