[new B+ tree] BTree nodes change order when promoted to root.
[new B+ tree] Cleanup.
Merge remote-tracking branch 'origin/new-index-structure' into new-index-structure
Merge remote-tracking branch 'origin/new-index-structure' into new-index-structure
Merge remote-tracking branch 'origin/new-index-structure' into new-index-structure
[new B+ tree] Added first version of CoW for ascending iterator.