Feature: transform state

For transforming persisted state, e.g. if a class has been renamed.

For reviewing, probably best to go through one commit at a time.

For the CLI support, this is really to get early feedback. It needs improvements, and I haven't written any docs.
good point.  OTOH entities usually refer to adjuncts, not the other way round, so not sure.  i think we fix this if we hit errors.  have added TODO in code:

        // TODO @neykov asks whether transformers should be run in registration order,
        // rather than in type order.  TBD.  (would be an easy change.)