Fix: utcnow is deprecated in Python 3.12 (#8)

- fixed `utcnow` deprecation warnings according to the [doc](https://docs.python.org/3.12/library/datetime.html#datetime.datetime.utcnow) 
- added pipeline for tests
- formatted code with Black formatter
- specified that the extension works with Python 3.8+

Merge pull request #5 from nzbgetcom/fix/release-dir

- fixed release-dir name
- updated "about"

Merge pull request #1 from nzbgetcom/feature/email-extension

- added EMail extension for NZBGet v22 and below