Proposal: Use furo theme for Sphinx docs about botan

[randombit]

No objection here

[mouse07410]

Does this add a dependency and require installing an extra Sphinx theme furo?

If so, shouldn't building.md tell that it's necessary for docs target, and how to install it?

[securitykernel]

It is not required. Just like before with the readthedocs theme, it will fall back to the agogo theme shipped with Sphinx automatically if furo is not found.

[lieser]

@randombit I would love it if the official Botan website could switch to this theme.
Currently it is only used as the default in the build scripts (if available), but not on the official site.

I think long sites like e.g. https://botan.randombit.net/handbook/api_ref/pubkey.html would benefit a lot of the better navigation via the sidebar that duro provides compared to the theme currently used.