Enhancement request: show packages

[trombonehero]

Since Graphviz supports clusters, it would be great if UMLGraph could show classes as belonging to packages. For example, when I have a project that extends classes in a library, it would be very useful to be able to put that library's classes inside of a box.

[dspinellis]

Thank you for the suggestion. I don't know anyone working on it, so feel free to implement it.