Maintenance release.
* Cleaned up license information.
* Fixed handling of status returned from `client_open` in examples.
* Converted comments into function docstrings in helper module.
* Reformatted source code with black and isort.
* Removed superfluous shebang lines and encoding declarations.
* Fixed typos in readme and changelog.
* Added Python 3.10 to list of supported versions in package meta data.