* Remove code with side effects from main When running tests withy pytest, some modules execute code in main scope and open plot or browser windows. Moves such code under `if __name__ == "__main__"`. * fixup! Format Python code with psf/black push
* added sol3.py for problem_20 * added sol4.py for problem_06 * ran `black .` on `\Python`
* #840 adds polymonial regression program in python * Update polymonial_regression.py * Update polymonial_regression.py