Make an illustrative change notes guide in GH UI

This change places a `README.rst` document under `changelog.d/` dir in
order for GitHub to render it when users navigate to this location via
the web UI.

It also includes that into the dev guide in Sphinx docs.

This type is more appropriate for snippets containing shell commands
with leading prompts followed by their output. `bash` syntax used
earlier treats everything as a raw shell script contents highlighting
words like `for`.

But only under Python 3.5!

This change adds a role that links to the GitHub user Sponsors
page. If that page is not set up, it'll redirect to the GitHub user
profile page instead:

Links to https://github.com/sponsors/{{ username }} open as GitHub
Sponsors page if the target `username` has it enabled and redirect
to https://github.com/{{ username }} if it's disabled.

Extract ppc patch

Adding changes to support PPC64LE

Apply docs revamp

Enable flake8 and cov plugins only when installed.

Add fallback for the situation where distutils.ccompiler.CCompiler.spawn has been patched. Fixes pypa/distutils#15.

Merge pull request #2381 from pypa/bugfix/2355-keep-distutils-patched-when-pip-imported-during-build

When pip is imported as part of a build, leave distutils patched.

Reduce size of setuptools' bdist_rpm._make_spec_file