Simplifing the CI/CD process

[davidsbatista]

• added GitHub workflows for:
  • code formatting
  • linting
  • type checking
  • tests
  • these all run everytime a PR is made - results here
• using pytest and coverage only instead of tox, since I think this lib is so simple - doesn't use any 3rd party libraries - running tests on a single python version should be fine, I propose 3.8
• added some nice badges to the README.MD
• removing all unnecessary files
• added a section on README.MD on how to contribute to the project
• increased the version to 0.2.0

NOTE: if this is OK I will then open another PR with an improved README.MD + some more examples on how to use the package

After it's approved we can also generate a new pip package + review the issues, I'm sure some will be closed/tackled.

[ivyleavedtoadflax]

This looks good. Just one query about the Makefile. Would be good to keep these recipes, and update them as appropriate.

[ivyleavedtoadflax]

I'd quite like to keep these recipes if we can because they do make life a lot easier. I think we definitely don't want to be managing requirements_dev.txt manually

[davidsbatista]

I can restore it for sure.