Add noindex and banner to older version documentations

[j-adel]

I'm not sure if others are getting the same experience, but when searching for Luxor.jl functions on a search engine like Google, usually the documentation on an older version comes up in the results. This is usually fine but sometimes it's very outdated. It is also not immediately obvious you're on an older version until you look at the version. I thought this was an issue in general with Documenter.jl, but according to the replies to this issue, looks like one could use the DocumenterTools.jl to update old generated docs to have noindex and a banner which would solve the aforementioned problems. I wouldn't mind making a PR but I wanted to make sure first that the maintainers are aware of this issue.

[cormullion]

Hopefully this will be easy when this Documenter issue or something similar is addressed.