Add tests and refactor for testing

[martialblog]

This PR adds unittesting and includes a small refactor for readability, testability and bugfixes

• Change output format (to enable formatting in Icinga2)
• Improve error handling except e: probably never worked
• Add testcases for all functions
• Refactor argparse for simpler testing
• Add linter and fix linting issues
• Add version output
• Add GitHub Action configuration
• Update .gitignore

[martialblog]

Name                   Stmts   Miss  Cover   Missing
----------------------------------------------------
check_mumble_ping.py      33      0   100%
----------------------------------------------------
TOTAL                     33      0   100%

🎤 ✋