Introduce comparing with namespace support.

src/rsm.rs

@@ -122,6 +122,7 @@ impl From<Set> for Element {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use compare_elements::NamespaceAwareCompare;
 
     #[test]
     fn test_simple() {
@@ -197,6 +198,6 @@ mod tests {
             max: None,
         };
         let elem2 = set2.into();
-        assert_eq!(elem1, elem2);
+        assert!(elem1.compare_to(&elem2));
     }
 }