use compositeUnsubscribe in combineAsArray
Call subscribe inside call to composite.add
Prefer referential equality over packing into Some
combineAsArray: indirection via markEnd and setValue doesnt really add clarity
combineAsArray: Factor out argument parsing
combineAsArray: Simplify subscription based on previous refactoring
combineAsArray: inline checkEnd function
Merge branch 'combineAsArray-composite'