• Add support for Python 3.12. With the removal of distutils from Python 3.12, projects
  using CFFI features that depend on distutils at runtime must add a dependency on
  setuptools to function under Python 3.12+. CFFI does not declare a runtime setuptools
  requirement to avoid an unnecessary dependency for projects that do not require it.
• Drop support for end-of-life Python versions (2.7, 3.6, 3.7).
• Add support for PEP517 builds; setuptools is now a required build dependency.
• Declare python_requires metadata for Python 3.8+. This allows unsupported Pythons
  to continue using previously released sdists and wheels.
• Move project source under src/; a more standard layout that also enables CI to more easily
  catch packaging errors.