Setuptools

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* Cleanup of setup.py script.

* Fixed documentation builders by allowing setup.py
to be imported without having bootstrapped the
metadata.

* More style cleanup. See 677, 678, 679, 681, 685.

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* 674: Default ``sys.path`` manipulation by easy-install.pth
is now "raw", meaning that when writing easy-install.pth
during any install operation, the ``sys.path`` will not be
rewritten and will no longer give preference to easy_installed
packages.

To retain the old behavior when using any easy_install
operation (including ``setup.py install`` when setuptools is
present), set the environment variable:

SETUPTOOLS_SYS_PATH_TECHNIQUE=rewrite

This project hopes that that few if any environments find it
necessary to retain the old behavior, and intends to drop
support for it altogether in a future release. Please report
any relevant concerns in the ticket for this change.

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* 398: Fix shebang handling on Windows in script
headers where spaces in ``sys.executable`` would
produce an improperly-formatted shebang header,
introduced in 12.0 with the fix for 188.

* 663, 670: More style updates.

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* 516: Disable ``os.link`` to avoid hard linking
in ``sdist.make_distribution``, avoiding errors on
systems that support hard links but not on the
file system in which the build is occurring.

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* 667: Update Metadata-Version to 1.2 when
``python_requires`` is supplied.

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* 631: Add support for ``python_requires`` keyword.