Include wrapper type when calling rust methods

Sometimes, when calling methods on a struct inside a box or rc, you want the wrapper object. The way to do it is to use `self: &Box<T>` notation in parameter. Here's an example.

use std::rc::Rc;
struct Node;

impl Node {
  fn test_rc(self: &Rc<Node>) {
    println!("test rc!");
  }
  fn test_box(self: &Box<Node>) {
    println!("test box!");
  }
}

fn main() {
  let n = Rc::new(Node);
  n.test_rc();
  let n = Box::new(Node);
  n.test_box();
}