Discovered in #378. `SigmaCollectionParseError()` is called on line 55 but it is never defined or imported which means that NameError will be raised instead of SigmaCollectionParseError.
Breaking change: Instead of feeding the output class with the results,
they are now returned as strings (*Backend.generate()) or list
(SigmaCollectionParser.generate()). Users of the library must now take
care of the output to the terminal, files or wherever Sigma rules should
be pushed to.