Merge a segment and its two flanking segments into one segment, and recalculating the segment statistics.
# S3 method for AbstractCBS
mergeThreeSegments(fit, middle, ...)Returns an AbstractCBS of the same class with two less segment.
An integer specifying the three segments
   (middle-1, middle, middle+1) to be merged.
Additional arguments passed to *mergeTwoSegments().
Henrik Bengtsson
Internally *mergeTwoSegments() is used.
  For more information see AbstractCBS.