Improvements
* 13 Added pyproject.toml and compliant PEP517/518
* 14 Several flake8 and black fixes
* 15 Migration from Travis to Github Actions
* 16 Added dynamic type checking
Breaking compatibilitty:
* Support for Python 3.5-3.6 was dropped and Python 3.8 was added.
* Function names changes from the releases 1.X, by convention, all words in method names are separed with _. Eg. naturalday is now natural_day.