Merge pull request dalek-cryptography#325 from rubdos/const_fn_for_sc…

…alar_from_bits

Make Scalar::from_bits a const fn.

src/scalar.rs

@@ -243,7 +243,7 @@ impl Scalar {
     /// This function is intended for applications like X25519 which
     /// require specific bit-patterns when performing scalar
     /// multiplication.
-    pub fn from_bits(bytes: [u8; 32]) -> Scalar {
+    pub const fn from_bits(bytes: [u8; 32]) -> Scalar {
         let mut s = Scalar{bytes};
         // Ensure that s < 2^255 by masking the high bit
         s.bytes[31] &= 0b0111_1111;