Add the undocumented Placeholder and two update URLs

http://asheiduk.de/post/fritzbox-dyndns/ and

https://service.avm.de/help/de/FRITZ-Box-Fon-WLAN-7490/018/hilfe_dyndns

The Update URL can contains a URL for the IPv4 and a second URL for the IPv6 Request. Splitted by a whitespace.