Allow results to be returned as an ArviZ InferenceData object
ArviZ provides a nice way to store and visualise samples from a variety of inference packages. It would be good to provide a method of the
Results class that converts the results to an Arviz
A more controversial suggestion would be to have the bilby
Results class actually itself be a child of the ArviZ
InferenceData class, but that would require a more considerable rewrite.