message: add instance to PartialOrd in the Special object
diff: @@ -66,7 +66,7 @@ impl<'a> AsRef<[u8]> for Bytes<'a> {
  fn as_ref(&self) -> &[u8] { self.0.as_ref() }
  }
  -#[derive(Debug, PartialEq, Copy, Clone)]
  +#[derive(Debug, PartialEq, PartialOrd, Copy, Clone)]
  pub enum Special {
  Bool(bool),
  Null,
  