Include pyproject.toml in sdist

Restore build-backend and remove switch to avoid pep517.

Co-Authored-By: Paul Ganssle <paul@ganssle.io>

Simplified mechanized release process through tox

fix support for easy_install's find-links option in setup.cfg

Merge pull request #1922 from benoit-pierre/fix_possible_issue_with_transitive_build_dependencies_from_extras

fix possible issue with transitive build dependencies

Rename 'Professional support' to 'For Enterprise' and add section on 'For Enterprise' to the README (linking to Tidelift).

Handle the case where a missing transitive build dependency is
required by an extra for an already installed build dependency.

wheel: fix `is_compatible` implementation

Add new hook 'setuptools.finalize_distribution_options'

Revert "drop easy_install script and associated documentation"

wheel: switch to `packaging.tags` for checking PEP 425 tags

This reverts commit 6e1838a9.