message: Add `Default` impl for `Queue`.
diff: @@ -81,6 +81,15 @@ struct Queue<M>(BinaryHeap<QueueEntry<M>>)
  where
  M: PartialEq + Eq + Ord;
  +impl<M> Default for Queue<M>
  +where
  + M: PartialEq + Eq + Ord,
  +{
  + fn default() -> Self {
  + Queue(Default::default())
  + }
  +}
  +
  impl<M> Queue<M>
  where
  M: PartialEq + Eq + Ord,
  