Support multiple versions

[Taucher2003]

When projects make a major version bump, we still need to be able to host the older versions of the docs.

[nicosammito]

Because we will publish our first 0.1.0 version of Pictor this week to start developing the landing page, we will need this asap.

[nicosammito]

Is this needed any longer, because for Pictor we switch to storybook static docs? Maybe some other repos need this...
@Taucher2003

[Taucher2003]

We probably still need this for our actual releases. But the priority is a lot lower now.