Improve coverage configuration

Use importlib instead of imp in __bootstrap__ functions

Remove pkg_resources.py31compat.makedirs() in favor of the stdlib

Fix exception causes in package_index.py

Unify the entry point template.

Fix entry point scripts

Decrease start-up time of editable-installed entry points on newer versions of Python

Defer finalize options

Avoid loading working set during `Distribution.finalize_options` prior to invoking `_install_setup_requires`, broken since v42.0.0. Fixes #2158.

DOC: Update mailing list link

Per https://groups.google.com/d/msg/pypa-dev/rUNsfIbruHM/LCEx-CB5AgAJ
the pypa-dev Google Group is now decommissioned.
Pointing to distutils-sig instead.
Signed-off-by: Sumana Harihareswara <sh@changeset.nyc>

In wheel-to-egg conversion, use simple pkg_resources-style namespace declaration for packages that declare namespace_packages. Fixes #2070.

DOC: fix link missing >

The `decalrative config`_ link present higher in the document is also
unresolved, I'm not quite sure what the intended target was.