Ineqpy

- worflows:
- use ubuntu-20.04 instead of latest (see https://github.com/actions/setup-python/issues/561)
- Fixed functions:
- concentration
- top_ratio
- add tests for:
- top_ratio
- hooover_index
- theil
- concentration

Added:

- top_rest ratio
- hoover index
- github actions for testing, upload wheels and generate docs

Updated:

- README
- documentation

Fixed

- All Survey's methods have been fixed.

This release include some bugfixes and increase the test coverage.

- Add src structure
- Add test suit for stats module
- Flake8 complaint
- Fix warnings from pandas and numpy