sled-search

Utility functions for searching a sled::Tree.
Includes:
search- allows for searching thesled::Treekey space using a guiding function.max- finds the greatest entry in thesled::Tree(usessearchinternally).pred- finds the greatest key preceding the given key (usessearchinternally).pred_incl- a version of thepredfn that is inclusive of the given key.