Tree traversal functions

[koraa]

We should provide functions for traversing trees make from containers that implement Get/Set

const treeGet = (seq, tree) => foldl(seq, tree, (c, k) => get(c, k));
const treeSet = (seq, tree, value) =>…
const tryTreeGet = (seq, tree, default) => // Returns default if a node didn't exist
const tryTreeSet = (seq, tree, value) => // Won't throw an exception if an intermediate node didn't exist
const treeCreateNodes = (seq, tree) => // Will create intermediate nodes (default values in sequence which is of the form [[key, defaultValue],...])