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.

This fixes a race condition in _bypass_ensure_directory where
two threads or processes may erroneously fail because they are
both creating the same directory. A more robust implementation
of this may involve exposing the un-wrapped os.makedirs.

Originally reported with proposed patch by @JonKohler in
github PR #1412. This patch came out of discussions on that
thread.

This mocks out the isdir call so that the directory is created
immediately after you determine whether or not it exists, thus
simulating a race condition between two threads or processes
creating the same directory.

fix #97 PEP420: find_packages()

Fix "Microsoft Visual C++ Build Tools" link