extend Python versions support

[afranck64]

The selected minimum Python version is 3.9 while versions 3.6 to 3.8 still account to more than ~80% of Python installations (for websites).

Dropping the encoding parameter for logging.basicConfig (or having a special handling for python>=3.9) and using string annotations for unions could help extend the supported versions.

[pythonbrad]

OK, thanks for this issue.
In function of the dependencies used, this will be the future requirements if the issue is solved.
Requires: Python >=2.7, !=3.0., !=3.1., !=3.2., !=3.3., !=3.4.*, <4