[Checkins] [zopefoundation/zope.interface] a800c4: Use C3 (mostly) to compute IRO.

[Jason Madden]

  Branch: refs/heads/issue21
  Home:   https://github.com/zopefoundation/zope.interface
  Commit: a800c40e39c374176f575c221cdc967f5481580a
      https://github.com/zopefoundation/zope.interface/commit/a800c40e39c374176f575c221cdc967f5481580a
  Author: Jason Madden <jamadden at gmail.com>
  Date:   2020-03-06 (Fri, 06 Mar 2020)

  Changed paths:
    M CHANGES.rst
    M docs/api/declarations.rst
    M src/zope/interface/declarations.py
    M src/zope/interface/ro.py
    M src/zope/interface/tests/test_declarations.py
    M src/zope/interface/tests/test_ro.py

  Log Message:
  -----------
  Use C3 (mostly) to compute IRO.

Fixes #21

The 'mostly' is because interfaces are used in cases that C3 forbids; when there's a conflict, we move forward by adding the simple legacy base to the list at the conflicting location and continuing.

I hoped the fix for #8 might shake out automatically, but it didn't.