Add {,de}serializer for VecMap

src/ser.rs

@@ -1,5 +1,5 @@
 use std::collections::hash_state::HashState;
-use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet};
+use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet, VecMap};
 use std::hash::Hash;
 use std::path;
 use std::rc::Rc;
@@ -587,6 +587,17 @@ impl<K, V, H> Serialize for HashMap<K, V, H>
     }
 }
 
+impl<V> Serialize for VecMap<V>
+    where V: Serialize,
+{
+    #[inline]
+    fn serialize<S>(&self, serializer: &mut S) -> Result<(), S::Error>
+        where S: Serializer,
+    {
+        serializer.visit_map(MapIteratorVisitor::new(self.iter(), Some(self.len())))
+    }
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 impl<'a, T> Serialize for &'a T where T: Serialize {