Adds networking library urnlib

This library implements the a class for representing an Uniform Resource Name (URN). It implements parsing and serialization according to the constraints defined in [RFC 2141](https://tools.ietf.org/html/rfc2141). It's released on [Maven Central](http://search.maven.org/#artifactdetails|de.slub-dresden|urnlib|1.0.0|jar) and aims to serve as a network identifier handling library just like the native Java URL and URI classes.

I'm not entirely sure `Networking` is the proper category, but I also don't see any other category it might fit.