Fixes #24: changes how the messages are displayed by returning the groups, line, column, severity, message_id and message
Fixes #26: deleted files are not considered in pre commit hook
Replaced assertEquals with assertEqual
Refactored test_gitlint.py
Improved gitlint test by checking output and added stdout and stderr args to gitlint.main
Changed e2e test to cal gitlint.main directly and fixed all the python3 errors surfaced because of that