Returns `true` if this list is an ordered link ```rust use orgize::{Org, ast::List}; let list = Org::parse("+ 1").first_node:: ().unwrap(); assert!(!list.is_ordered()); let list = Org::parse("1. 1").first_node:: ().unwrap(); assert!(list.is_ordered()); let list = Org::parse("1) 1\n- 2\n3. 3").first_node:: ().unwrap(); assert!(list.is_ordered()); ```
(&self)