Clean-py

Slightly improved `setup.py` by refactoring it and using `find_packages()`.

Specified the required `click` library version to be 7.0, the latest version that enables `clean_ipynb` to color some output messages.

Added `--version` flag.

Removed shorter aliases for all flags.

Improved description.

A cleaned `.ipynb` is saved in the default `.ipynb` `JSON` format, which uses the indent size of 1 and overall a bit strange. Yet, this update is valuable because it minimizes the `diff` between a cleaned `.ipynb` and its original.

First release :)

`clean_ipynb` is working.

I hope many people use and improve this tool.