Anonymize IP addresses

I implemented an option to anonymize IP addresses before writing them to the log.
This is needed in some countries like Germany because there you are not allowed to save any personal data (to which IP addresses count) of your visitors unless they explicitly agree.

From IPv6 addresses the first two segments are retained. (recommended by the [data protection supervisors of germany and it's federal states](http://www.bfdi.bund.de/SharedDocs/Publikationen/Entschliessungssammlung/DSBundLaender/82DSK_IPv6.pdf?__blob=publicationFile ))
From IPv4 addresses the first two octets are retained. (seems sensible to me)

The code is mostly straight-forward, the only thing I am not sure about is if the monitor can cope with the truncated addresses. (3905aac)