lib/tree: add checks for leaf node link node types
lib/tree: fix map leak in check_node_leaf
lib/tree: fix bounds issues in *_shift_*ward
lib/tree: don't shift if leaf is empty in leaf_shift_*
lib/tree: adjust checks in leaf_shift_* and leaf_zero
lib/tree: rearrange functions
lib/tree: handle empty nodes properly in tree_graph_r
lib/tree: add item_qty to tree_graph
lib/tree: adjust tree graphics in tree_graph
lib/tree: fix leaf_shift_backward
lib/tree: fix new node count after split
lib/tree: make retry an integer in tree_insert
lib/tree: update branch_shift_* to match leaf_shift_*
lib/tree: add tree_retrieve
lib/tree: improve node search algorithms (normal, hypo, branch)