Unify Tip vs Batch formats

[bartelink]

This consists of two elements, as described in #50:

• Move all events into e arrays
• take advantage of the reduction of clashing names to apply the following renames:
  • compaction events -> unfolds
  • creation date/time -> t
  • unfold/domain event union case/event type (was et, presently t): t -> c(ase)

There is some ugliness that drops off in #48 if we adopt this too