NWD v2.1.0

General code cleanup, PEP compliance, and type hinting.

Fixes minor bugs related to email delivery.
Fixes a minor bug that could prevent the correct completion time from being recorded.

Adds the exit code of the process to the notification message, when available.

Initial release after the Python 3 rewrite

Complete rewrite from the old Perl script.
E-mail credentials are now stored on the system keychain.
Switched from libnotify to GTK+ notifications on Linux.
Experimental support for Windows.