Openfisca-core

Technical changes

- Switch CI provider from CircleCI to GitHub Actions

Bug fix

- Fix the collection of OpenFisca-Core tests coverage data
- Tests within `openfisca_core/*` were not run

New Features

- Add group population shortcut to containing groups entities

New Features

- Introduce `openfisca_core.types`

Documentation

- Complete typing of the commons module

Dependencies

- `nptyping`
- To add backport-support for numpy typing
- Can be removed once lower-bound numpy version is 1.21+

- `typing_extensions`
- To add backport-support for `typing.Protocol` and `typing.Literal`
- Can be removed once lower-bound python version is 3.8+

Documentation

- Complete the documentation of the commons module

Bug Fixes

- Fix doctests of the commons module

Dependencies

- `darglint`, `flake8-docstrings`, & `pylint`
- For automatic docstring linting & validation.