* Remove support for installing via ocamlfind.
* Remove PREFIX.
* Move the source of MenhirLib into lib/.
* Move the source of MenhirSdk into sdk/.
* Build and install everything using dune.
* Run all tests using dune. Reorganize the test directory.
* Move the old ocamlbuild demos to a subdirectory.
* Introduce [make versions] to test Menhir with multiple versions of OCaml.
* Update the release scripts.

which produces a token [SEMI]. The parser SEMI to appear in three places:
after a declaration; after a rule; after a producer. Only two grammars in
the test suite have required changes.

as we need to annotate it with `%unreachable`
to declare that it is okay if it is unreachable.

Add a link from the manual to `standard.mly` in the repository.

New options --coq-lib-path and --coq-lib-no-path control this behavior.

(These options are not yet implemented.)

Documentation: document the use of ocamlbuild.
The upcoming interaction with dune is not yet documented.

In theory, the two are not quite equivalent when surrounded by
whitespace. In practice, I didn't see a difference.

The documentation used @[ everywhere, whereas the correct syntax is [@.