Define and add setup.py file about catnip

[zmaalick]

Useful resources:

https://docs.python.org/3/distutils/setupscript.html
https://docs.python.org/3/distutils/introduction.html#distutils-simple-example
https://packaging.python.org/tutorials/packaging-projects/
Sample: https://github.com/pypa/sampleproject/blob/master/setup.py
List of options: https://pythonhosted.org/an_example_pypi_project/setuptools.html

for registration: https://the-hitchhikers-guide-to-packaging.readthedocs.io/en/latest/quickstart.html