Pprint3x

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2023-07-14:
- flake8
- remove some tests for underscore numbers

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2023-07-14:
- add codeql badge
- move 3rd_party_stubs outside the src directory
- add pypy 3.10 tests
- add python 3.12-dev tests

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2023-07-13:
- require minimum python 3.8
- remove python 3.7 tests

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2023-07-13:
- introduce PEP517 packaging standard
- introduce pyproject.toml build-system
- remove setup.cfg
- remove setup.py
- update black config
- clean ./tests/test_cli.py
- remove travis config
- remove bettercodehub config
- remove "better code" badges
- remove python 3.6 tests
- adding python 3.11 tests
- update pypy tests to 3.9

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2022-06-02: update to github actions checkoutv3 and setup-pythonv3

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2022-06-01: update github actions test matrix