Implement an option to show dependencies between modules only

[MSoegtropIMC]

This PR adds an option to show dependencies between modules - that is all nodes and edges with the same module path are coerced into one. This is useful to analyse large projects.

Note that module dependencies can somehow by cyclic (not sure why but I saw one case in CoRN) which the existing transitive reduction code could not handle, so I replaced it with the transitive reduction function from the Graph library.

I did run make test and see 3 deviations, but I see the same deviations in coq-master with 8.20. One is about renaming Coq to Rocq, the others are likely cause by changes in the standard library.

[ybertot]

I am currently studying this pull request. I think we should add some documentation in the README.md file and some tests. I will do it when I have time, but don't hesitate adding stuff in this regard if you have some handy.

[MSoegtropIMC]

Thanks! For sure I can add documentation and tests. I am also thinking about some extensions, say grouping modules by module path prefix and some options on which part of the module path is shown in the graph, but this can also be done in a second step.