Upgrade packaging to 16.8

Add python_requires to setup.py

Make Entrypoint methods docs up to date.

Fix #849 global-exclude globbing

package_index: fix bug not catching some network timeouts

Use super to resolve the superclass, but fall back to direct access on Python 2 where old style classes are used. Ref #843.

Remove _add_defaults_data_files override and add unittest

Merge branch 'suppress-warning' of https://github.com/abstrus/setuptools into abstrus-suppress-warning

Entrypoint.load() is deprecated and it's recommend to use `require` and
`resolve` separately.

After #764, `global-exclude .pyc` no longer excluded `.pyc` files.
This fixes that regression, and adds a test for this behaviour.