v6.4.0

• compatibility adjustments for setuptools >58
• only put minimal setuptools version into toml extra to warn people with old strict pins
• correctly handle hg-git self-use
• better mercurial detection
• modernize packaging setup
• python 3.10 support
• better handling of setuptools install command deprecation
• consider pyproject.tomls when running as command
• use list in git describe command to avoid shell expansions while supporting both windows and posix
• add --strip-dev flag to python -m setuptools_scm to print the next guessed version cleanly
• ensure no-guess-dev will fail on bad tags instead of generating invalid versions
• ensure we use utc everywhere to avoid confusion