There needs to be a "revision_history" function on the
VERSION_REPOSITORY<T> type to support EHR_Extract requests for
revision histories rather than (or with) actual data. There should
probably be a new REVISION_HISTORY class added. This needs to have
the information of VERSIONs and VERSION_AUDITs without the actual
data; probably the attestations should be included.

The EHR_EXTRACT specification would also need to be changed to
support revision history requests, probably by adding the ability
to have a revision history in an X_COMPOSITION.

DK: I am not sure what use case this serves: I am trying to think
of a scenario when version information would be requested without
the data to which this pertains.

TB: this is very common in software version control - the need
to look at a revision history without looking at the data to
which it pertains.