tests: fix some pytest warnings under Python 2

Merge pull request #1867 from benoit-pierre/drop-some-pkg_resources-tests-dependency-on-easy_install

test: drop pkg_resources tests dependency on easy_install

improve workaround for #1644

Fix empty namespace package wheel install

Remove "upload" and "register" commands.

The upload and register commands were deprecated over a year ago, in
July 2018 (PR GH-1410, discussed in issue GH-1381). It is time to
actively remove them in favor of twine.

Upgrade setuptools.depends to importlib from depracated imp

Fix code for detecting Visual Studio's version on Windows under Python 2.

pkg_resources: fix ``Requirement`` hash/equality implementation

Document using asterisk in package_data section

docs: drop ez_setup documentation and related references

doc: drop most references to EasyInstall

Add Python 3.8 final to Travis test matrix

Fixes for python3.10

Improve Visual C++ 14.X support