Added mode to differentiate set/state type features.
Merge pull request #377 from ambiata/topic/mode

Added mode to differentiate set/state type features.
First phase of naive set support.

This just ignores prioritization of facts with a Set mode.
Support latest expression on single struct field
Merge pull request #378 from ambiata/topic/sets-one

Sets - Part One
Merge pull request #334 from ambiata/topic/latest_struct_value

Support latest expression on single struct field
One line oversight on Latest Reducer PR
Added snapshot with V0 to data-regression
Added another ingest with V0
Minor adjustments
Spec to check that incrementals get used