Marie Helene Kvello-Aune

Add API methods for removal of primary and secondary IPv4 and IPv6 addresses. See ifconfig's keyword "-alias".

Implement API methods to allow setting interface address and subnet mask/prefix, as done by ifconfig's "inet + netmask" and "inet6 + prefixlen" keywords.

Once system integration tests (#14) are in place, it'll be possible to automatically detect memory leaks using something like [Valgrind](http://valgrind.org/).

Create integration tests for the various parts of the API. Current examples code is a good starting point, but needs to be expanded. Look into what framework the FreeBSD project...