Heading slugs could be friendlier

[dleeftink]

When linking to headings on a Framework page, slugs are generated in a manner inconsistent with other static site generators/GitHub.
For instance, when linking to a heading in a source file on GitHub will make the link incongruent with the page URL slug under the current sanitisation scheme:

https://github.com/suptext/suptext.github.io/blob/main/code/from/2024/07/26/building-quickset.md#whats-your-path

https://suptext.is/from/2024/07/26/building-quickset#what%E2%80%99s-your-path%3F

Instead of:

https://suptext.is/from/2024/07/26/building-quickset#whats-your-path

I think the way GitHub sanitises heading slugs is the way to go.

[mbostock]

There’s no guarantee we’ll match whatever GitHub does, but we can explore making friendlier slugs. We use markdown-it-anchor.

https://www.npmjs.com/package/markdown-it-anchor#user-friendly-urls