Add example showing graph generation for module dependencies

[arporter]

I've been trying to find ways of investigating the module dependencies in NEMO. I've not had a lot of success so far but I have generated a new example (based on @hiker's for doing Makefile deps) that constructs a graph in dot. This can then be rendered in e.g. https://github.com/graphia-app/graphia:

I'll add the script to do this under examples.

[arporter]

I should say the current example is based on @ZedThree's https://gist.github.com/ZedThree/7196938#file-fortran-dot-graph-py which I now realise doesn't have a license :-( I'll have to create a new implementation, perhaps following what is done in Habakkuk.