These are the current numbers on release:

```
 261K -- dist/wacoq_worker.js
 369K -- dist/frontend/index.css
 583K -- dist/frontend/index.js
```

Seems to work! I guess it can be done better, but for now that is OK.

This is a large build-time improvement, moreover we can get rid of a
lot of troublesome code regarding how to manage assets.

`esbuild` has proven a great tool so far.

Tested with both backends.

We still keep the CLI and the WASM backend on webpack, the idea is
to move them to esbuild in subsequent commits.

CLI should use a native Coq instead, it is super-slow.

We also disabled the `collab` and `ide-project` builds for now,
re-adding before merging hopefully.

The compatibility story with user .html pages needs to be revised,
IMHO as this is a foundation for the LSP backend this is the time to
drop support for some patterns we had in the past.

Borrowed from #275

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

We also move from hacks to a proper config object (which can be
properly created in a dynamic top-level context).

Also, note that we now use a ES6 map for the routes, this is more
convenient to add / remove elements than using the bare object.

Disabled `strictNullCheck`, because it's too hard to
satisfy at the moment.

So that we can create both jsCoq and waCoq packages.

Also, support for importing legacy `_CoqProject` definitions.

Ported old code to TypeScript with major rearrangement.
Build based on Webpack.