wheel: fix `is_compatible` implementation

Add new hook 'setuptools.finalize_distribution_options'

Revert "drop easy_install script and associated documentation"

wheel: switch to `packaging.tags` for checking PEP 425 tags

This reverts commit 6e1838a9.

Add support for `license_files` option in metadata

drop easy_install script/command, re-implement `fetch_build_egg` to use pip

Move all finalization of distribution options into hooks. Allow hooks to specify an index for ordering.

tweak workaround for #1644

Work around buggy pip detection code for "pip.exe install/update pip ...".

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