Feature request - Implement GVPR.

[larssb]

Had the issue of nodes with no edges in a generated graph. I would like to be able to give the users of Out-PSModuleCallGraph the option of excluding such nodes. Reading up on the documentation of Graphviz I found that the tool GVPR should be able to do this. Do you already have implementing GVPR on the to-do list for PSGraph? If not I would like to request it. I could also help out by trying to integrate it into PSGraph if okay with you @KevinMarquette

Thank you and looking forward to your response.