Upgrade to full application

[dylanbmorgan]

Update the repository from a testing script to a full application for performing core hole spectroscopy simulations. This will also be a great opportunity for me to learn about packaging. Current TODOs are tracked here:

• Finish updating the code
• Implement new click options into the projector function/command
• Test the latest code and try and find edge cases
• Organise python files into a src directory
• Create a tests directory
• Use Poetry to set up the package. Use this page for reference: https://python-poetry.org/docs/cli/
• Possibly incorporate setuptools https://setuptools.pypa.io/en/latest/userguide/index.html
• Re-write force_occupation module