Constant TREE_SHORTCUTS_TEXT

pub const TREE_SHORTCUTS_TEXT: &str = r"type TreeHandle = Option<Rc<RefCell<TreeNode>>>;
type ORRT = Option<Rc<RefCell<TreeNode>>>;
type RRT = Rc<RefCell<TreeNode>>;
type RT = RefCell<TreeNode>;";

Easy-to-input typedef of some tedious, but also useful structures