Add a documentation version selector

[SuperFola]

We can handle multiple versions for the documentation on the website but we have no way to jump around.

Python has this selector:

We could easily add one too, by generating a JSON structure to store the current version (latest) and the available ones, upon generating a new version:

{
  "latest": "v4.5.6",
  "all": ["v.1.2.3", "v2.3.4", "..."]
}