Update README.md

Adjust declaration of time_relative(time) (iiasa#551)

Mark v3.4.0 in release notes

Mark v3.3.0 in release notes

Mark v3.3.0 in release notes

Merge pull request iiasa#463 from iiasa/publish-workflow

Add "publish" CI workflow

Release v3.2.0

Prepare v3.1.0

Update test_cli.test_dl() to use __version__

Complete v3.0.0 migration notes