* Initialize a tleaf iterator by giving its depth, levels arity and iteration policy.
* "it": a tleaf iterator
* "depth": the total number of levels of the tree, including leaves
* "arity": An array of size (depth-1). For each level, the number of children attached to a node. Leaves have no children, hence last level arity is ignored. Arities are organized from root to leaves.
* "arity": An array of size (depth-1). For each level, the number of children attached to a node.
* Leaves have no children. Arities are organized from root to leaves.
* "index": NULL or an array of depth excit_t to re-index levels.
* It is intended to prune node of certain levels while keeping index of the initial structure.
* Ownership of index is not taken. The iterator allocates a copy of index and manage it internally.
* "policy": A policy for iteration on leaves.
* "user_policy": If policy is TLEAF_POLICY_USER, then this argument must be an array of size (depth-1) providing the order (from 0 to (depth-2)) in wich levels are walked.
* when resolving indexes. Underneath, a product iterator of range iterator returns indexes on last levels upon iterator queries. This set of indexes is then