better offsets take 2

The current wording of offsets would create situations where it would be impossible to tell if an offset is an integer offset or a special value of some other type that happened to be an integer

This PR introduces a `continueFrom` parameter as a third offset parameter (the first two being offset ant page) that avoids this problem. It also adds the comingFrom value to use to the metadata returned with results, simplifying use of this parameter for end users.