Migrate "Find directed cycles"

[clue]

Migrate graphp/graph#113 (refs graphp/graph#119)

[dav-m85]

Since there's a dependency against graphp/graph#112, it would make no sense to port it now regarding composer.json constraints (we got separated projects).

That being said, graphp/graph#112 is really small and not BC break, it's sad directed cycle research algorithm is stopped only by this.

[clue]

Thanks for keeping this updated, indeed, makes sense to tackle graphp/graph#112 first.