Improve dyndns compliance

[f03el]

• Use return codes from https://help.dyn.com/remote-access-api/return-codes/
• Use FQDN instead of only the updated hostname in the request

Not sure if you want these changes, but I had problems using ddclient before, since it expects proper response codes in return. Regarding the FQDN, that seems to be the standard. I also had to remove the timing message, since that extra information doesn't seem to fit in well with a standard compliant response.

[ethanpil]

Looks good. Thanks!

[f03el]

Good! Thanks for a nice tool!