Allow SharedSecret to be created from byte array

This was accidentally removed in 8b2edad. See also the discussion
on #402

src/ecdh.rs

@@ -71,6 +71,11 @@ impl SharedSecret {
  pub fn secret_bytes(&self) -> [u8; SHARED_SECRET_SIZE] {
  self.0
  }
+
+ /// Creates a shared secret from a byte serialization.
+ pub fn from_bytes(bytes: [u8; SHARED_SECRET_SIZE]) -> SharedSecret {
+ SharedSecret(bytes)
+ }
 }
 
 impl Borrow<[u8]> for SharedSecret {