#78 Support IPv6 at FreeDNS

[David]

I offer up the attached patch to provide support for IPv6 at FreeDNS. This also fixes bug 63 and bug 74 reported here. My patch is inspired by that posted here https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=704467 but with enhancements to make it more robust and useful. Namely...

use= and usev6= may be specified together for the same host name or either one may be specified on its own so can simultaneously update A and AAAA records for the same interface/host.
IPv6 address can also be specified within the conf file if desired.

For a system inside NAT you might specify use=web and usev6=if and both the A record and AAAA record at FreeDNS will be updated.
Alternatively you could just specify usev6=if and the A record will not be updated... making the assumption that the NAT gateway took care of that for you.
On a device connected directly to the public internet you could specify use=if and usev6=if.
You can hard code the IPv6 address inside the conf file with usev6=ip and ipv6=<whatever></whatever>

Options for usev6 are either if (interface) or ip (ip address specified in conf file with keyword ipv6=). Other options (like web or cmd) are not supported.

Only FreeDNS is supported... I leave other services up to someone else to tackle.

DAK