#206 Add certfp support.

[Valentin Lorentz]

Hi,

Certfp is a way to authenticate to servers without any password; it is only based on certificate fingerprint.

A few networks support it (only freenode and oftc, as far as I know), but it is a nice feature anyway.
https://github.com/ProgVal/Limnoria/commit/e65a722b2f6d09dc082dd7646327b487ac4244b5

Regards,
Valentin