Connect over IPv6

An effort to solve https://github.com/embolalia/willie/issues/187.

When connecting to myircserver.example.org I confirmed works over IPv6, but additional testing is needed to confirm it still works on IPv4. Possible test cases are:
- [x] ipv6 client to ipv6 server
- [x] ipv6 client to ipv4 server
- [x] ipv6 client to dual stack server (hostname with both AAAA and A records), possible special case with fallback when the AAAA record is broken
- [x] ipv4 client to ipv6 server (show a proper error?)
- [x] ipv4 client to ipv4 only