New supported formats: some suggested by [rt #44067 - Michael
Reddick], while others have been independently added.Fix a regression [rt #44691 - Jason May].
Shift common conversion logic within base calculation methods
to the grammar class.Introduce a helper class for handling actions related to
metadata flags and to serve as container for setter/checker
methods.Wrap Decode_Month() in Compat.pm.
Test both implementations within each method in Compat.pm.
Preserve order of tests.
Add a test-file for regressions.
Remove the obsoleted internal use of a total-modified counter.