Breaking Changes

• KeyEvaluation has been renamed to ScanEvaluation.

• All scan() functions have been updated with the node_evaluatorcallback
  now returns aScanEvaluation instead of a bool. To preserve existing
  behavior, returnScanEvaluation::ReadDatainstead of true and
  ScanEvaluation::Stop instead of false.

  The new functionality unlocked with this change is that scan operations can
  now be directed as to whether to skip navigating into an interior node. The
  new reduce() function uses this ability to skip scanning nodes when an
  already reduced value is available on a node.

Added

• TreeFile::reduce(), Tree::reduce(), TransactionTree::reduce() have been
  added as a way to return aggregated information stored within the nodes. A
  practical use case is the ability to retrieve the number of alive/deleted keys
  over a given range, but this functionality extends to embedded indexes through
  the existing Reducer trait.