git hook code formatting

* git hook can run some script files before or after a command such as commit or push
* using that we may enforce code formatting rules
* [Davi](https://medium.com/zyseme-technology/code-formatting-scalafmt-and-the-git-pre-commit-hook-3de71d099514), [Bangar](https://medium.com/@harshitbangar/automatic-code-formatting-with-git-66c3c5c26798)
* ipynb files may include results; it may not be exactly necessary to keep track of them as they could be automatically generated
* However, for review purposes, it might be helpful
* What would be more desirable?
* For this repository (not forks) clearing the output before commit might be helpful