IRCv3.1 base compatibility

I am primarily asking this for SASL, but it requires CAP and by adding multi-prefix (handling that nick can be opped and voiced and more at the same time) you are IRCv3.1 base compliant.

• http://ircv3.net/specs/core/capability-negotiation-3.1.html
• http://ircv3.net/specs/extensions/multi-prefix-3.1.html
• http://ircv3.net/specs/extensions/sasl-3.1.html

It would be nice if other IRCv3 capabilities could be added if they are any use to biboumi. Especially useful would be SASL 3.2 reauth which allows you to be identify if services are down for initial connect or other cases that are currently only handled by certfp.

For rest of the specification, please see http://ircv3.net/irc/.