A complete active pattern that extracts the kind and data from a `DataSegment`
 value. This makes it easier to write functions that only need data:

    let sumAny = function DataSegment.Any(_, data) -> Stats.sum data

 Complete active pattern that makes it possible to write functions that behave
 differently for complete and incomplete segments. For example, the following
 returns zero for incomplete segments:

     let sumSegmentOrZero = function
       | DataSegment.Complete(value) -> Stats.sum value
       | DataSegment.Incomplete _ -> 0.0