Belated release of master from 2021

Apologies to all for the delays to this release.

This is a release of the state of master following changes in May to August of 2021 with passing tests and due caution that I can't remember what I was holding off on to put this release out at the time. Probably something I wanted to include, but didn't get a chance to go back to including.

A new maintainer has been added to tfenv and I hope to make progress on the outstanding Issues and PRs soon.