DONE - use pathlib.Path to handle paths instead of os.path.*
DONE - use tempfile.TemporaryFile in tests to avoid having to clean up files after
DONE - make exception messages more specific (such as including information about bad inputs, etc)
DONE - add tests for writing both yaml and json
DONE - in Writable.write(..), derive file format from file ext, else use the given format
DONE - where applicable, make enum classes private, (for example, GridType becomes _GridType, and under the class Grid, add the class var GT5 = _GridType.GT5 ... )
DONE - change ValueErrors to TypeErrors where applicable
DONE - change MetadataMixin.add_metadata() to be add_metadata(self, *args, **kwargs)
DONE - when testing constructors, add assertions
DONE - for unit tests that check for raised exceptions, verify the raised exception message