devel/ocaml-res: massage the port in preparation for OCaml 4.06+

- Update to version 5.0.1, adjust LICENSE, take maintainership
- Now builds itself with Dune (devel/ocaml-dune): GC no longer
  useful USE_OCAML_* and configure-related knobs; build process
  is now also jobs-safe because of this
- Project had moved to GitHub: switch to USE_GITHUB and update
  WWW line in the port description
- Convert to static pkg-plist to make tracking changes easier