PEP-518/pyproject.toml support

[birdcolour]

Hi, absolutely love the tool! My team are absolutely hooked on Jupyter notebooks, and this is a really great way for me to start getting the review/refactoring process back under control 😄

Would you accept a PR that implements support for loading the configuration data from a project's pyproject.toml file, i.e. PEP-518 as an alternative to the jupytext.toml file? If so, I would be happy to try and contribute it!

(edit - wrong PEP)

[mwouts]

Thank you @birdcolour , yes sure that would be awesome!

The functions that we use to find out and load the configuration files are in config.py, and some tests on these configuration files are in tests/test_config.py, tests/test_cm_config.py (for use within Jupyter) and in tests/test_cli_config.py (at the command line).