Support for match-case statements

[cookiepresence]

Match statement support had been missing in astor, and is only recently added: berkerpeksag/astor#219. However, this will come at the cost of diverging from the PyPI version.

[sakehl]

Sorry for taking a while to respond.

Anyway I looked into this, and I added a commit that uses the latest astor version.

https://gitlab.tue.nl/jupyter-projects/nb_mypy

Some quick test make it look at that match case statements work completely fine.

The only thing is that I am unable to make this into a new PyPi package, since PyPi does not support "direct links", i.e. any dependencies should be on PyPi. So you can install it manually, but not via PyPi.