Flask-digestauth

Various fixes, with the help from SonarQube.

* Added log out support. User can log out.
* Added on-login event handler. You can do some accounting when the user logs in.

This release was written in Sydney and on the international flight, and released in Taipei.

Changed the minimal Python version to 3.7.
Released at Sydney, Australia on vacation.

The initial release.
Released at Sydney, Australia on vacation.