Can this be released with v5.1.1?

Suggestion: There are two definitions of __ne__, one for date and one for datetime class. They are buggy; removing both should resolve the issues. (Python's default behavior is to fall back to __eq__ when __ne__ is not defined.) This approach will reduce code duplication and prevent future errors, in my opinion.

Thanks @5j9 for your great suggestion! I didn’t implement the __ne__ method in the #159 for that reason, but I missed its implementation in the date class.
This method has now been removed from both classes.

Thanks @mobinghoveoud 🎉 !