- update to version 1.20.0
- set default python to python3
- fix tox python3 overrides
- Update reno for stable/queens
- pypy is not checked at gate
- Trivial: Update pypi url to new url
- Update links in README
- Remove setting of version/release from releasenotes
- remove obsolete tox environments
- Switch to stestr
- Updated from global requirements
- add lower-constraints job