Python 3 and APIv5 rewrite (Live DNS)

[ORelio]

Hello,

Since I've accidentally migrated my domain to APIv5, I've rewritten the script to work with Python 3 and the newer API v5 instead of API v4. Public IP is retrieved through icanhaz.

Fork is available at: https://github.com/ORelio/gandi-dyndns-v5

This pull request also includes changes from my previous PR that implements icanhaz and fixes a small bug that prevents record update in IPv4+IPv6 mode when only one IP address has changed : #17