We reorganize jsCoq's source code as to be more modular, in particular
we start to place backend files under the `backend` directoy, and
frontend files under `frontend`.

Code as it now does work, note however that still quite a bit of work
is needed. In particular, the headless frontend should get its own
directory, the coq-jslib directory should go away, use more types,
etc...

This is just the actions table from the landing page, with
appropriate formatting borrowed.

To avoid confusion, `ui-js/jscoq.js` has been renamed.
Also, a legacy-mode `jscoq-loader.js` that emulates the old behavior.

This requires renaming of webpack.config.js to indicate it is a
CommonJS module system.

We do some extra fixes for the webpack build to work.

We use a strategy top-down to convert to modules. For now we convert
the loader to a module. This requires a few minor changes, but
shouldn't be too hard.

Hopefully this fixes #278

Probably should not have been there in the first place; also, interferes
with packaging
(due to `-` in dir name).

With jsCoq SDK.

Uses a stylesheet borrowed from Pandoc.

 * In OPAM 2.1 it seems that space-separated package names are obsolete.
   Using comma, which seems to also work with 2.0.8.
 * Specified that Node.js >= 16 is required (for CLI).

Filled in the links in the navbar, etc.
Added hover action to quick-start reference.

- Migrated patches for 8.14.
- Up wacoq to 8.14 in docker image
- install: 8.14 requires `coq-core` and `coq-stdlib` to be installed.
- Set version 0.14.0.

So that we can create both jsCoq and waCoq packages.

Some of the instructions are duplicated from the README, but that's ok.
The manual is not yet complete with all the features, but at
least addresses #207.

Closes #207.

This should nicely support M1-based OSX ; unfortunately, it required
loosening the constraint on `ppx_deriving_yojson` as to make it
co-installable with `ppx_import`, but that's a minor issue.

Note the new option system for OCaml Opam packages, thus selecting a
32bit compiler is done differently now.

We also bump some other libraries as to reduce non-deterministic
developer switches.

Nothing too remarkable, code-wise, but a big change upstream is the
addition of `zarith` as a hard dependency.

TODO:

- update addons

Coq standard library is now bundled in the `'coq'` package bundle.

Fixes #210.

Thanks to enjoysmath, closes #206

I have done a quick pass and tried to tidy the readme up a bit.

Please don't hesitate to further refine.

`Ltac2` is pretty light (<=200Kb) and it doesn't depend on anything,
so it seems convenient for the user to have it around.

This should fix #124 , however addons that are not using Dune
still do need that the whole build is performed under the correct opam
switch.

**Important**: math-comp addon has been re-named to `mathcomp`, there
was some ambiguity before, but now we prefer mathcom as done in the
`From mathcomp` prefix.