Added unit tests for canonicalization and fixed several bugs therein
flake8 and regexp cleanups
Unskip test and fix the expected value -- it's a bit nonsense tbh
Add test fixtures for relaxed, haphazardly generated from dkimpy.
Merge remote-tracking branch 'dreid/dkim' into dkim
Implemented relaxed canonicalization
Document relaxed canonicalization
Merge branch 'pr/43'