IPv6 Support

[lemoer]

I locally hacked the IPv6 support by changing the following line:

- self.irc = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+ self.irc = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)

But this is not a nice solution since the library now has no more option to connect to an IPv4 server. It would be nice, if the library would be able to handle both IP versions automatically.

Ideas:

• Use ipaddress.ip_address(self.network).version to determine the IP version (if self.network is an IP-Address)
• Use the dns result for hostnames (by prefering IPv6 over IPv4)

[fenhl]

@lemoer Thanks for the suggestion, I have now implemented this. If you find any bugs, please do open issues for them, as I currently don't have the time to test this.