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The broken link used to point to Python 2 docs (which has been moved).
Since Python 2 has reached its end-of-life, link to Python 3 docs instead.

Copy docs requirements to a separate file due to RTD constraints.

Copy docs requirements to a separate file due to RTD constraints. Fixes #2001. Ref readthedocs/readthedocs.org#6662

Pin virtualenv to <20 as workaround for #1998.

Avoid installing setuptools 45 on Python 2.

Because Requires-Python is disabled for Python 2 to allow this declared-incompatible version to install on Python 2, the build-requirements must exclude installing setuptools 45 during the build-system setup.

Because Python 2 tests are only needed for internal validation, and because the latest pip is already installed, the build-system can rely on `backend-path = ["."]`.

Fixes #1996.

Deprecated Eggsecutable Scripts

Bootstrap the environment in tox, allowing simple 'tox' to run tests and simplifying all of the pipelines.

Make easy_install command less strict (fixes #1405)

Fix install_scripts() if bdist_wininst is missing

Move test dependencies to package metadata.

Closes #1985

Move docs dependencies into package metadata and use same technique as jaraco/skeleton to build docs in tox and rtd.

Improve tests setup in GH Actions CI/CD workflow

Opt into PEP 517 for pip installs to avoid implicit dependency on Setuptools to install test dependencies.

Move test dependencies into the package, removing 'tests' directory which masks the error reported in #1896.

Rewrite selective PIP_IGNORE_REQUIRES_PYTHON to allow test dependencies in metadata to be installed without ignoring REQUIRES_PYTHON

As per #1961.

P.S. Using `contains(['2.7', 'pypy2'], matrix.python-version)` does not
work even though
https://help.github.com/en/actions/automating-your-workflow-with-github-actions/contexts-and-expression-syntax-for-github-actions#contains
promises arrays to be supported.