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