Txaio

------

- fix: support for Python up to v3.11
- fix: update GitHub CI
- fix: copyright transferred to typedef int GmbH - no license change!

------

- fix: cancel handling in python 3.8/3.9. (175)
- fix: gracefully fail if coroutine called with wrong args (176)
- fix: eliminate redundant dep. on mock (170)
- fix: doc note that twisted supports native coroutines (172)

------

- fix: update minimum dependencies (here, and in other crossbar packages) in an attempt to tame the new pip dep resolver madness.

-------

- new: CI/CD migrated to GitHub Actions
- new: support Python 3.9 (CI / testing added)
- new: minimum Python version is now 3.6

------

- new: upload wheel to S3 (bucket "crossbarbuilder") in CI deploy stage
- fix: fix event loop threading issue (PR 163)

------

- new: support import-time framework selection
- fix: remove python2 support (finally)