SASL Auth

[meskarune]

Add support for SASL auth to the bot.

Here is the spec: https://ircv3.net/specs/extensions/sasl-3.1.html

Steps to authenticate successfully (and assuming no ircd errors):

1. Bot sends CAP REQ :sasl
2. Listen for a CAP ACK :sasl
3. Send AUTHENTICATE PLAIN if ACK comes back
4. Wait for an AUTHENTICATE + response
5. Send AUTHENTICATE <base64 encoded 'username\0username\0password'> SASL PLAIN request
6. Wait for a 903 :SASL authentication successful response
7. Send a CAP END message

Each step would need its own error handling and then fallback to nickserve auth or just have users set which auth method to use.

[meskarune]

This feature depends on the bot's ability to respond to events other than privmsg, so I guess it's blocked until the event reaction stuff is reworked.