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/templates/shared/_footer.html.j2

@@ -1,10 +1,14 @@
-    <footer>
-      <div class="container">
-        <p>This website is made with <a href="http://getbootstrap.com">Bootstrap</a>, themed with <a href="https://bootswatch.com">Bootswatch</a>.</p>
-        <p>jq is licensed under the MIT license (code) and the <a href="https://creativecommons.org/licenses/by/3.0/">CC-BY-3.0</a> license (docs).</p>
+    <footer class="bd-footer bg-body-tertiary">
+      <div class="py-3 text-center">
+        <p>
+          This website is made with <a href="https://getbootstrap.com" target="_blank" rel="noopener">Bootstrap</a>,
+          themed with <a href="https://bootswatch.com" target="_blank" rel="noopener">Bootswatch</a>.
+        </p>
+        <p>
+          jq is licensed under the MIT license (code) and the
+          <a href="https://creativecommons.org/licenses/by/3.0/" target="_blank" rel="noopener">CC-BY-3.0</a> license (docs).
+        </p>
       </div>
     </footer>
-
-    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
-    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js" integrity="sha256-Sk3nkD6mLTMOF0EOpNtsIry+s1CsaqQC1rVLTAy+0yc= sha512-K1qjQ+NcF2TYO/eI3M6v8EiNYZfA95pQumfvcVrTHtwQVDG+aHRqLi/ETn2uB+1JqwYqVG3LIvdm9lj6imS/pQ==" crossorigin="anonymous"></script>
-    <script src="https://twitter.github.io/typeahead.js/releases/0.11.1/typeahead.bundle.js"></script>
+    <script src="https://cdn.jsdelivr.net/npm/bootstrap@5.3.1/dist/js/bootstrap.bundle.min.js"
+      integrity="sha384-HwwvtgBNo3bZJJLYd8oVXjrBZt8cqVSpeBNS5n7C8IVInixGAoxmnlMuBnhbgrkm" crossorigin="anonymous"></script>