Implement Hash for ByteOrder types

The absence of these impls lead to the absence of `Hash` for the
byteorder-aware numeric types.

Fixes #1871

src/byteorder.rs

@@ -63,6 +63,7 @@
 use core::{
     convert::{TryFrom, TryInto},
     fmt::{Binary, Debug, LowerHex, Octal, UpperHex},
+    hash::Hash,
     num::TryFromIntError,
 };
 
@@ -81,7 +82,7 @@ use super::*;
 ///
 /// [`U32<BigEndian>`]: U32
 pub trait ByteOrder:
-    Copy + Clone + Debug + Display + Eq + PartialEq + Ord + PartialOrd + private::Sealed
+    Copy + Clone + Debug + Display + Eq + PartialEq + Ord + PartialOrd + Hash + private::Sealed
 {
     #[doc(hidden)]
     const ORDER: Order;
@@ -104,7 +105,7 @@ pub enum Order {
 /// Big-endian byte order.
 ///
 /// See [`ByteOrder`] for more details.
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
 pub enum BigEndian {}
 
 impl ByteOrder for BigEndian {
@@ -121,7 +122,7 @@ impl Display for BigEndian {
 /// Little-endian byte order.
 ///
 /// See [`ByteOrder`] for more details.
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
 pub enum LittleEndian {}
 
 impl ByteOrder for LittleEndian {