Repository cleaning tasks

[pchlap]

• [ ] make pylint pass (rename variables + function + class names)
• [x] add docstrings for all functions + classes
• [x] rename/move modules where needed
• [x] add unit tests (with synthetic data)
• [x] auto generate docs and run unit tests on GitHub
• [x] update README
• [x] Freeze and clean up 3rd party library requirements
• [ ] make all functions support pathlib Path
• [x] Strip content from Jupyter notebooks on commit
• [x] clean example Notebooks with description and link to Google Colab
• [x] Update Jupyter notebooks to use new TCIA downloaded data
• [x] Render Jupyter notebooks for docs using nbshpinx