Add more tests to doc test

Author: mankinskin

src/lib.rs

@@ -1739,6 +1739,8 @@ pub trait Itertools : Iterator {
     ///
     /// let numbers = [1, 2, 3, 4];
     /// assert_eq!(numbers.iter().find_or_last(|&&x| x > 5), Some(&4));
+    /// assert_eq!(numbers.iter().find_or_last(|&&x| x > 2), Some(&3));
+    /// assert_eq!(std::iter::empty::<i32>().find_or_last(|&x| x > 5), None);
     /// ```
 	fn find_or_last<P>(mut self, predicate: P) -> Option<Self::Item>
 		where Self: Sized,