Merge #674: Derive Hash for Scalar

f87dc91 Derive Hash for Scalar (Jiri Jakes)

Pull request description:

  Unless there is some safety concern I cannot see, having Scalar implementing Hash would be useful.

ACKs for top commit:
  Kixunil:
    ACK f87dc91
  apoelstra:
    ACK f87dc91

Tree-SHA512: 276670a3d938fade3828123547b01e38b1a3c56775fb3c545d2c392622de808cf2bf8125925c7896ee27bacd5897d88908384d8c157dc8ec7d605781475964fd

src/scalar.rs

@@ -22,7 +22,7 @@ use crate::constants;
 // Internal represenation is big endian to match what `libsecp256k1` uses.
 // Also easier to implement comparison.
 // Debug impl omitted for now, the bytes may be secret
-#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd)]
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
 pub struct Scalar([u8; 32]);
 impl_pretty_debug!(Scalar);
 impl_non_secure_erase!(Scalar, 0, [0u8; 32]);