Added SASL support

[gsf]

Set sasl: true in options, along with nick, userName, and password,
for SASL login (required for some IP ranges for connecting to
Freenode, etc.).

No docs or tests, sorry. Happy to provide if you give some guidance.

[quentinxs]

While I applaud your effort, you may want to rework your code a bit as CAP is/ can be used for more than SASL. Other than that, documentation is as easy as updating docs/API.rst to reflect your changes to the library.

[gsf]

Yes, I was kind of greedy with the CAP signals since nothing else in the library is using them yet. The third commit makes it more specific. When a use case comes up for other CAP functionality it can be accommodated then.

The last commit adds the option to the docs.

If these additions don't hinder other uses, I would really appreciate their inclusion. I can't connect to Freenode via my phone without them (anything on the T-Mobile network is subject to SASL).

[gsf]

I could also move those listeners into the if ( self.opt.sasl ) block so that they only exist when SASL is enabled.

[kamaln7]

👍

[martynsmith]

This looks fine, I notice that we get fairly wildly varying coding styles, I think I might get some jshint config set up and try to get everyone to conform to that :-)

[gsf]

Thanks for merging this in!