Think of how Jupytext might use this

[choldgraf]

@mmcky 's comments about jupytext made me have a thought. Apologies if this has been obvious to others the whole time, but I think that this tool could be useful for Jupytext as well. It is common that people want to write their notebook content in text files, but view them in a notebook interface. For this, jupytext does a great job (e.g. in jupyterlab you can double-click a jupytext markdown file, and it'll open as a notebook even though it's still saving back to that markdown file).

However, one issue with only having a markdown file is you have no place to put the outputs. For users that don't want to have a 'paired' ipynb file on disk the whole time, perhaps Jupytext could leverage jupyter-cache to insert the outputs into the notebook when it is being rendered in the interface. This way you could cleanly separate outputs and content, similar to how we plan to do with Sphinx.