Allow more control over head tags in HTML output

[videah]

Forgive me if this is not the case, but at the moment I don’t think there is any way to add anything into which I’m finding a little restrictive when it comes to external scripts, fonts, meta tags, open graph tags etc.

[breezykermo]

Yes, this is something I'd like to add. I'd welcome a thoughtful PR on this front. I would want to first check that there is no way to do this in Typst itself, as I suspect that some of the recent changes around the #document function might have enabled it, and then what the plan is in Typst's HTML export roadmap for this. Ultimately I am almost certain that this will be native in Typst, and so if we do introduce a 'polyfill' in the meantime, I would want it to be as close to what we expect the native application will be as possible.

[breezykermo]

Since 0.2.0, there is not a simplified entrypoint in crates/html/src/lib.rs that shows more clearly how the html plugin injects CSS and JS into the document head. For the html format in particular, we want to add the infrastructure for another kind of plugin that represents an 'augmentation', allowing some custom function in Typst to map to some custom JS/CSS/web element.

As noted in my previous comment, we hope that this is soon possible natively in Typst. This kind of Rheo 'component' could, for example, be written using the new bundle format which the html crate in Rheo could then register and inject appropriately into the final site.

There is still a little bit of thinking to be done on how to make this work, though.