Version picker for the docs (sphinx extension)

[nicolan]

Cyrus has a number of different versions that we maintain concurrently (for varying values of 'maintain').

At the moment there is 2.5 (old stable, most users are still on, some bugfixes getting backported), 3.0 (stable, not yet widely adopted), master (development) and sort of 2.4 (old old sunset stable, only emergency security fixes).

We want to be able to provide easy access to the different versions of docs on the website. At the moment this is accomplished via urls www.cyrusimap.org/ (where version is 2.5, 3.0 (alias stable) and dev). Each version has its own directory on the web server.

Goal: have a version picker like on sphinx-doc.org that toggles the versions for you without having to scrabble around with the urls. This version picker needs to be present across all versions of Cyrus docs.

[elliefm]

The place for most of this to live is probably going to be in the cyrusimap.org repository (https://github.com/cyrusimap/cyrusimap.org), rather than the cyrus-imapd repository. That way it can sit across all versions independently of them, and doesn't need to be precariously maintained across a bunch of different branches.

[nicolan]

I think I can build this myself now.