Public facing zome functions needs stability

[8e8b2c]

In the following commit I inadvertently removed an interface that was being used by nor-backend's document publisher:

9ecf37f#diff-96fcb355ac41cefcf5fafeffa68461e84e343aa321bc505da4098d050138ace0L57

The code should be organised to better reflect which function signatures are public facing, and therefore likely to have dependants.

[8e8b2c]

This pattern does something to make public facing interfaces more explicit:
#98