services: Add anonip-service-type.
* gnu/services/web.scm (anonip-configuration): New record type.
(anonip-configuration?, anonip-configuration-anonip,
anonip-configuration-input, anonip-configuration-output,
anonip-configuration-skip-private?, anonip-configuration-column,
anonip-configuration-replacement, anonip-configuration-ipv4mask,
anonip-configuration-ipv6mask, anonip-configuration-increment,
anonip-configuration-delimiter, anonip-configuration-regex): New procedures.
(anonip-service-type): New service type.
* doc/guix.texi (Log Rotation): Add subheading for Anonip Service.