Update Python version support.

[icemac]

• Configuring for pure-python
• Update Python version support.

open issues:

• find out why coverage has dropped drastically.
  • seems like

    zope.pytestlayer/src/zope/pytestlayer/tests/test_integration.py

    Lines 52 to 55 in a14fbe8

    	process = subprocess.Popen(
    	cmd,
    	stdout=subprocess.PIPE,
    	stderr=subprocess.STDOUT)

    ignores coverage settings so theses calls are not under coverage