Add bleeding edge API documentation to rtd

[Kijewski]

Resolves #362.

[Kijewski]

@GuillaumeGomez, I disabled the option to force-push or ignore the CI in the settings. (After accidentally force-pushing to the old repo.) I hope that's OK. If there is a dire need to ignore the CI or do a force-push, then it's just one click to disable the guard.

[GuillaumeGomez]

I think it's a good idea. Force push is a very big power to have, some might even say too big. 😆

Anyway, looks good to me, thanks!

[Kijewski]

I forgot to update the API hook, so the version was not built automagically, but triggering the build manually worked: https://askama.readthedocs.io/en/latest/doc/askama/index.html. :)