the wheel package is not required to build a source distribution

Resolves #1474.

Fix for Unicode handling in PEP 518 backend

setuptools: fix regression with `egg_info` command

Ensure version is tagged only once.

Prepare 40.1.0

Add an empty .gitignore to changelog.d to prevent the directory from
being deleted when it is emptied out during a release.

Support for scripts with unicode content

This also renames the _to_ascii function to better reflect its purpose.

Upgrade vendored appdirs from 1.4.0 to 1.4.3

Upgrade vendored PyParsing from 2.1.10 to 2.2.0

* fix #1419 PEP420: add find_namespace: directive

* fix #1419 PEP420: add find_namespace: directive to documentation

* fix #1419 PEP420: add tests

* fix #1419 PEP420: clean up code

* fix #1419 PEP420: fix typo in documentation

* fix #1419 PEP420: fix typo in documentation

* fix #1419 PEP420: clean up code

* fix #1419 PEP420: add changelog entry

* fixup! fix #1419 PEP420: add tests

* fix #1419 PEP420: cleanup code refactor markers

* #1420: Rename find_namespace_ns to find_namespace_packages

*  #1420: update changelog entry

tox: fix configuration so newer tox versions are supported

Starting with tox 3.2.0, the commands for installing/listing
dependencies changed from pip to python -m pip, which is problematic
as this will leave bits of the previous (from the virtualenv creation)
older version of setuptools installed in the site-packages directory
because from pip's point of view, the active setuptools version is the
one in the current directory (which cannot be uninstalled).

Fix #1453.

Remove spurious executable permissions

Egg race condition

Switch over to using six.PY{2,3} when possible

* Add a space after header, so reST rendering isn't mangled.

* Add newline in template, too.