Upstreamable items

[bsipocz]

I open this issue to track issues we run into that should actually live upstream. Preferably edit the checklist.

• caption hackery from tox.ini for the rendered pages should be an upstream configurable
• we should note forced to convert md to ipynb to be able to run pytest flavour of testing.
  - for a recap: we want to buy into the pytest ecosystem as it provides a lot of nice features for testing, e.g reporting on cell level, nice tracebacks in the logs, warning handling, enabling to use other pytest plugins, etc.
• First TOC item must be a file -- why? these restrictions don't feel great (I run into them in both the repos I was trying to switch to the new stack)