Pyopenair

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* **fix** : Fix missing AL value when no miminal altitude (default is 'AL SFC')

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* **refactor** : Improve code quality
* **test** : Add pytest tests
* **test** : Add CI

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* **fix** : floor feet altitude for lower bouds
* **test** : add pytest to deps
* **fix** : fix comment formatter
* **docs** : Update README
* **chore** : Change build tools from `setuptools <https://pypi.org/project/setuptools/>`_ to `poetry <https://python-poetry.org/>`_.