Migrate to blake2b_simd and blake2s_simd crates

The primary reason for migrating is that these crates provide APIs for
setting the personalisation string. This enables us to depend solely on
published crates, and thus publish our own crates.

The SIMD implementations are ported from libsodium.

Closes #67.

sapling-crypto/src/circuit/blake2s.rs

@@ -320,13 +320,13 @@ pub fn blake2s<E: Engine, CS: ConstraintSystem<E>>(
 
 #[cfg(test)]
 mod test {
+    use blake2s_simd::Params as Blake2sParams;
     use rand::{XorShiftRng, SeedableRng, Rng};
     use pairing::bls12_381::{Bls12};
     use ::circuit::boolean::{Boolean, AllocatedBit};
     use ::circuit::test::TestConstraintSystem;
     use super::blake2s;
     use bellman::{ConstraintSystem};
-    use blake2_rfc::blake2s::Blake2s;
 
     #[test]
     fn test_blank_hash() {
@@ -392,7 +392,7 @@ mod test {
 
         for input_len in (0..32).chain((32..256).filter(|a| a % 8 == 0))
         {
-            let mut h = Blake2s::with_params(32, &[], &[], b"12345678");
+            let mut h = Blake2sParams::new().hash_length(32).personal(b"12345678").to_state();
 
             let data: Vec<u8> = (0..input_len).map(|_| rng.gen()).collect();