Consider/evaluate MyST-NB or jupyter-sphinx to combine OpenMS and pyopenms documentation

[jpfeuffer]

Other advantages:

• get rid of "half-manual" notebook conversion process and the notebook-branch
• no updating of plots and generated pictures anymore
• no "output" codeblocks necessary anymore
• we can showcase equivalent C++ code with a cling kernel (maybe not side-by-side/tabbed as I hoped, at least with MyST-NB https://github.com/executablebooks/MyST-NB/issues/265)

See: https://myst-nb.readthedocs.io/en/latest/index.html and https://github.com/executablebooks/jupyterlab-myst on the binder side

Or: https://jupyter-sphinx.readthedocs.io/en/latest/ (not sure if compatible with binder, since it has own code execution with thebelab)