Instead of `.cjs`; enough with this nonsense.

- don't rebuild the cli stuff when the frontend/backend changes
- make tests work again

This is not perfect but it works (and it is much faster).

For some reason I couldn't make `fflate-unzip` work with ESBuild, so
I've placed a copy and tweaked the exports.

All wasm binaries are read from `node_modules` directly, so there is no
need for a `bin/` directory (this was a hack).

The deps are collected in a meta-package `wacoq-deps`, which is
published to NPM separately and should not change often.

The wasm backend bytecode is now loaded
from `backend/wasm` (and also linked
accordingly).

Will gradually move parts from the other repo, wacoq-bin, to `backend/wasm`.
This will allow some code reuse between the backends.

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 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.

So that we can create both jsCoq and waCoq packages.

This is phrased as an "addon"; I think that not only libraries can be
"addons" but this kind of interop UI functionality should be as well.

It does not mean that UI addons should be built outside of the jsCoq
source tree like mathcomp & co.
If they are small enough, they are ok where they are in `ui-js/addon`.

What was needed in order to run unit tests in Node.js is
now located in `headless.ts`.
It is invoked via the regular CLI (bundled with Webpack).

Fixes #195.

32-bit compilation is using switch jscoq+32bit. 64-bit compilation
is using jscoq+64bit.
Coq is cloned into _vendor+xxx directories by Coq version and word
size, and so are add-ons.

This is a workaround suggested by @ejgallego to solve an issue where
Dune failed to build after `make links` was run.

We port the build system to Dune. This setup will integrate nicely
with Coq 8.10, but until this arrives it also provides a few
advantages:

- better `.merlin` files, automatically generated,
- clean build tree: all the artifacts go under _build,
- modular organization of the development: we introduce a separate
  library for the JS Coq package manager.

Note indeed that now all the build artifacts do live in
`_build/default`; `make links` will allow you to serve pages in-tree.

Pending:

- fully split the libmngr build to its own repository.
- libjs: implement recursive scan / get closer to Dune.

Enhanced the log icons, which were cropped.
Added Coq and Github icons in toolbar.

JsCoq now runs in a worker and communicates with coq-manager using
messages and PPX serializers.

We have reshaped the API quite a bit. We are very close towards
convergence with SerAPI, from which we have imported quite a few ideas.

The main changes are:

- coq-manager now follows a fully reactive approach (as suggested by
  @cpitclaudel) The document model has also evolved.

  This implies a big improvement in ease of document handling. In
  particular, we do not wait for `Add`, we listen to feedback to color
  states, and we use the new `Cancel` API instead of `EditAt`.

- The library manager is basically shared with serapi, and it has been
  greatly simplified.

- The protocol features a more robust initialization procedure, even
  if a bit heavier on client side responsibilities.

- We have removed jsmock, it is not useful anymore.

Many, many hacks have been removed in favor of more principled
solutions; still, we have quite a long way to go.

This commit improves #13, helps a bit with #9 (now we can kill the web
worker), and (in an non-optimal way yet) fixes #16.

Pending items:

+ Pp.t rendering is just a prototype, we need to improve it and insert
  divs following the current box mode.

+ Pp.t normalization leaves a lot to be desired. We can likely
  normalize it Ocaml-side and produce a div. We could even use jsoo's
  Tyxml for that.

- The invalidation, focus, and movement logic needs a bit more of
  work. In particular we need to streamline adding many sentences.

Real interaction with the worker is pretty fine these days.

- We allow to export the initial namespace as implicit.

  This will help closing #18.

  In general, it was an annoyance for the users, so we may follow
  upstream on this one for now. We will update collacoq to use the
  proper default, and keep the init page with the more lightweight
  setup.

Unfortunately we are using some bad hacks...

We now load the libraries from a json file. We have 3 categories,
plugins, standard coq libraries and addons.