Deprecate argot documentation

[XVilka]

Now BAP supporting building documentation with odoc, I think it is safe to drop the argot support, which last time was updated in 2012 (mainstream), and only receives fixes from you. Odoc is actively maintained, and simply has prettier output. I suggest to make it official documentation builder. Moreover, they are working on integration of it with mdx so the examples in the documentation can be built and tested. See https://github.com/ocaml/odoc/blob/bb539dbe6892f0c9d9c8a487b9af1dbddf4cb1c2/notes/testable_examples.md and ocaml/odoc#303 for more information