Fallback Behavior for Versions

[arnavs]

See JuliaLang/www.julialang.org#204

[mortenpi]

It's a bit tricky to achieve, but could be doable by having Documenter maintain a sitemap of some sort in the root directory, similar to the version.js file.

[odow]

I'm doing a triage of open documenter issues and closing issues that are stale. If I've made a mistake, please re-open

Closing as stale. I understand the motivation, but it is tricky and has a lot of edge-cases. For example, there's no guarantee that the page exists on different versions, and even if it doesn't there's no guarantee that it links to the same content. So it seems much simpler just to go back to the home page.

[mortenpi]

Actually, let me reopen this. I think this might be doable with some JS, if we'd do a HEAD call to check if a page with the same URL exists under the other version (if it does, go there, if it doesn't, go to root like now). The version selector needs JS anyway.