Make the change type be generic over any T rather &T (#31)

This makes the interface of this crate more flexible as the utility
methods such as `iter_changes` now also work if a container does not
contain references.

src/common.rs

@@ -159,3 +159,27 @@ pub fn group_diff_ops(mut ops: Vec<DiffOp>, n: usize) -> Vec<Vec<DiffOp>> {
 
     rv
 }
+
+#[test]
+fn test_non_string_iter_change() {
+    use crate::ChangeTag;
+
+    let old = vec![1, 2, 3];
+    let new = vec![1, 2, 4];
+    let ops = capture_diff_slices(Algorithm::Myers, &old, &new);
+    let changes: Vec<_> = ops
+        .iter()
+        .flat_map(|x| x.iter_changes(&old, &new))
+        .map(|x| (x.tag(), x.value()))
+        .collect();
+
+    assert_eq!(
+        changes,
+        vec![
+            (ChangeTag::Equal, 1),
+            (ChangeTag::Equal, 2),
+            (ChangeTag::Delete, 3),
+            (ChangeTag::Insert, 4),
+        ]
+    );
+}