State row fields

These fields identify a state row and describe how it changed from the earlier inventory.

Field	Type	Unit	Meaning
sparklogs.data.instance	string		The row's subject id, echoed onto the row so a table entry identifies itself without reference to the key it was built from.
sparklogs.data.delta_kind	string		What happened to this row: added, changed or removed. Delta rows only.
sparklogs.data.delta_old	object		The full row as it was before the change, rather than a field-level diff: that is the question people ask, and the diff is derivable from it while the reverse is not. Delta rows only.