AVL Tree Map / Set in Rust

An ordered map / set implemented with an AVL tree (nearly balanced binary search tree) in Rust.

```Rust use avl::AvlTreeMap;

let mut map = AvlTreeMap::new(); map.insert(0, "zero"); map.insert(1, "one"); map.insert(2, "two"); asserteq!(map.get(&1), Some(&"one")); map.remove(&1); assert!(map.get(&1).isnone()); ```

This is solely to get practice with the dark art of unsafe Rust. For all common purposes one of the standard library collections should be preferable.