Add support for multiple domains.

dyndns-client has been updated to support creation and updating of
multiple domains. See dyndns.cfg.example for the new configuration
syntax.
Add support for root domain updates.

Allow setting an A record for the root of a zone. e.g. if working with
the zone example.com, adding :example.com to the records parameter in
the config file will create or update an A record for example.com.
Merge branch 'multi-record'