Fix flakiness in SnapshotReducerSpec
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
Fixed ChordFacts expected to respect sets
Update dictionaries due to introduction of mode
Added check from tombstone in LatestStructReducer
WIP: SquashChordReducerState
Reduction logic for squashing chord