Redesign website (#2628)

* Bump up Bootstrap to v5.3.1, Bootstrap Icon to v1.10.5.
* Use autoComplete.js to drop dependency on jQuery and typeahead.js.
* Support dark mode.
* New svg logo and icon with responsive color mode support.
* Normalize section ids to lower kebab-case for easiness of linking.
* Use relative paths for links for local development (--root /output).
* Various markup cleanups and accessibility improvements.

docs/README.md

@@ -11,16 +11,16 @@ need `python3` and `pipenv`. You can install `pipenv` like so:
 
 Though, you may need to say `pip3` instead, depending on your system. Once
 you have `pipenv` installed, you can install the dependencies by running
-`pipenv sync` from the `docs` directory.
+`pipenv sync` from the `docs/` directory.
 
 Also, you may need to run `virtualenv -p /usr/bin/python3 venv/` and
 then `source venv/bin/activate`, and only then `pipenv sync`.
 
 Once this is done, rerun `./configure` in the jq root directory and then
-the Makefile will be able to generate the jq manpage.  You can also just
-run `pipenv run build_manpage.py` in the `docs` directory to build the
-`jq.1` page manually, and `pipenv run build_mantests.py` to build the
-contents of `tests/man.test` and `tests/manonig.test`.
+the `Makefile` will be able to generate the jq manpage.  You can just run
+`make jq.1` to build the manpage manually, and `make tests/man.test` to
+update the manual tests.
 
-To build the website, run `pipenv run ./build_website.py` from inside
-the `docs` directory.
+To build the website, run `pipenv run python3 build_website.py --root /output`
+in the `docs/` directory. To serve them locally, you can run
+`python3 -m http.server`.