Improve CI and docs

[romangg]

• Become REUSE compliant again
• Add a funding file
• Add badges to readme
• Generate coverage report and submit to Codecov

[codecov[bot]]

Welcome to Codecov :tada:

Once merged to your default branch, Codecov will compare your coverage reports and display the results in this comment.

Thanks for integrating Codecov - We've got you covered :open_umbrella: