Simplify exampleSite setup

Use a replace directive in exampleSite/go.mod to point to the directory above instead of the themesDir workaround it replaces. This should make it more robust and be the same setup as people using this theme for real projects.

netlify: Bump to Hugo 0.91.1

Also remove the usage of getenv in the example site.

Add x-cloak to body to prevent flicker on load

Fix language filter on load

Fixes bep#74

Remove unused JS code

js: Remove unused function

Fix TOC rendering issues

While rendering TOC, some items were lost. For example:

- if last h1 has some children or grand children
- if any h1 has multiple h2 (without any h3)

Signed-off-by: Khosrow Moossavi <[email protected]>

Update theme.toml

Bump y18n from 4.0.0 to 4.0.1

Bumps [y18n](https://github.com/yargs/y18n) from 4.0.0 to 4.0.1.
- [Release notes](https://github.com/yargs/y18n/releases)
- [Changelog](https://github.com/yargs/y18n/blob/master/CHANGELOG.md)
- [Commits](https://github.com/yargs/y18n/commits)

Signed-off-by: dependabot[bot] <[email protected]>

Pin the jQuery to the 3.41 tag