Other potential bandaids to pull off before v1.0.0

[ml-evs]

This issue can be used to track any big sweeping changes we want to make before v1.0.0.

I think the most pressing one would be finally splitting the package up into namespace packages so that models, reference server, validator and client code can be installed and versioned independently of one another, from the same repository (see #609 and #255 for previous discussion).