Use dataclasses publicly

[johndoknjas]

Start using the dataclasses introduced in #144 publicly. I.e.:

• Replacing dict args and return vals of public functions.

Obviously many/all of these will technically be breaking changes, so some consideration will be needed. We don't want changes to have a good chance of failing silently for existing users.

[gameroman]

I think we can do something similar to get_parameters

[johndoknjas]

@gameroman Yup, though probably not needed for all cases. A soft problem I haven't been able to solve is how to deal with running out of function names :)

[gameroman]

I am thinking we could probably make dataclasses to be a subtype of a dict with its methods overriden