Update README example with new iterators

.rustfmt.toml

@@ -2,4 +2,7 @@ fn_brace_style = "SameLineWhere"
 fn_return_indent = "WithWhereClause"
 fn_args_density = "Compressed"
 where_layout = "Horizontal"
-format_strings = false
+format_strings = false
+chain_one_line_max = 15
+ideal_width = 100
+take_source_hints = true

README.md

@@ -44,19 +44,11 @@ fn main() {
     tree.insert(Node::new(3), UnderNode(&child_id)).unwrap();
     tree.insert(Node::new(4), UnderNode(&child_id)).unwrap();
 
-    println!("Pre-order:");
-    print_pre_order(&tree, &root_id);
-    // results in the output "0, 1, 3, 4, 2, "
-}
-
-fn print_pre_order(tree: &Tree<i32>, node_id: &NodeId) {
-    let node_ref = tree.get(node_id).unwrap();
-
-    print!("{}, ", node_ref.data());
-
-    for child_id in node_ref.children() {
-        print_pre_order(tree, &child_id);
+    println!("Post-order:");
+    for node in tree.traverse_pre_order(&root_id).unwrap() {
+        print!("{}, ", node.data());
     }
+    // results in the output "0, 1, 3, 4, 2, "
 }
 ```
 

src/tree/mod.rs

@@ -1252,9 +1252,10 @@ impl<T> Tree<T> {
     fn insert_new_node(&mut self, new_node: Node<T>) -> NodeId {
 
         if self.free_ids.len() > 0 {
-            let new_node_id: NodeId = self.free_ids
-                .pop()
-                .expect("Tree::insert_new_node: Couldn't pop from Vec with len() > 0.");
+            let new_node_id: NodeId =
+                self.free_ids
+                    .pop()
+                    .expect("Tree::insert_new_node: Couldn't pop from Vec with len() > 0.");
 
             self.nodes.push(Some(new_node));
             self.nodes.swap_remove(new_node_id.index);