Restructure as a Python package

[wtbarnes]

Fixes #77
Fixes #100
Fixes #101

This PR restructures the entire repository as a Python package using pybind11. This supersedes #79.

Remaining TODOs:

• Apply the OA package template
• Return a Python dictionary containing all results
• Allow for passing in inputs directly rather than using a config file
• Implement user-facing API for specifying inputs
• Add docs section summarizing versions of EBTEL and explaining advantages of ebtel++
• Move old configuration docs to docstrings, mostly of model classes
• Convert old md examples to gallery entries
• Add docs page on ebtel++ equations (moved to Update documentation to include EBTEL equations with area expansion and two fluid effects #96)
• Setup RTD build
• Update GHA to actually run the tests
• Fix Windows tests (moved to Fix Windows installation on CI #100 )
• Update GHA to build wheels for all platforms (moved to Update CI to build wheels for all platforms #101)
• Update README
• Understand why yum install boost-devel hangs
• Understand compilation failure for intel macos

[nabobalis]

Do you want to enable nitpicky? Maybe not in this PR tho.

[wtbarnes]

Yeah I'll leave it to a subsequent PR.

[nabobalis]

Enable all of them!

[nabobalis]

A few comments/questions but looks good to me.

I did not review the Python code or the docs that closely. I have some personal formatting issues for the examples but its so minor it isn't worth the time.

[wtbarnes]

A few comments/questions but looks good to me.

I did not review the Python code or the docs that closely. I have some personal formatting issues for the examples but its so minor it isn't worth the time.

Thanks! Always happy to do a more thorough review of the examples later on down the road. The existing examples were adapted from my old mkdocs page. I'm going to leave future and improved examples to future PRs.