Re-organize and clean-up code to meet coding standards

[tloubrieu-jpl]

1. Organize code as a python package so that it can be tested and packaged with:
   $ python setup.py test
   $ python setup.py sdist bdist_wheel

2. use the libraries standard for PDS dev (e.g. requests instead of urllib)

3. break the code into sub-modules and files,

Associated requirements:
🦄 #16