Create a dedicated crate for the DKG (#141)

* Add dkg crate

* Remove F_len and G_len

They're generally no longer used.

* Replace hash_to_vec with a provided method around associated type H: Digest

Part of trying to minimize this trait so it can be moved elsewhere. Vec, 
which isn't std, may have been a blocker.

* Encrypt secret shares within the FROST library

Reduces requirements on callers in order to be correct.

* Update usage of Zeroize within FROST

* Inline functions in key_gen

There was no reason to have them separated as they were. sign probably 
has the same statement available, yet that isn't the focus right now.

* Add a ciphersuite package which provides hash_to_F

* Set the Ciphersuite version to something valid

* Have ed448 export Scalar/FieldElement/Point at the top level

* Move FROST over to Ciphersuite

* Correct usage of ff in ciphersuite

* Correct documentation handling

* Move Schnorr signatures to their own crate

* Remove unused feature from schnorr

* Fix Schnorr tests

* Split DKG into a separate crate

* Add serialize to Commitments and SecretShare

Helper for buf = vec![]; .write(buf).unwrap(); buf

* Move FROST over to the new dkg crate

* Update Monero lib to latest FROST

* Correct ethereum's usage of features

* Add serialize to GeneratorProof

* Add serialize helper function to FROST

* Rename AddendumSerialize to WriteAddendum

* Update processor

* Slight fix to processor

crypto/ciphersuite/src/dalek.rs

@@ -0,0 +1,44 @@
+use zeroize::Zeroize;
+
+use sha2::{Digest, Sha512};
+
+use group::Group;
+use dalek_ff_group::Scalar;
+
+use crate::Ciphersuite;
+
+macro_rules! dalek_curve {
+  (
+    $feature: literal,
+
+    $Ciphersuite: ident,
+    $Point:       ident,
+    $ID:          literal
+  ) => {
+    use dalek_ff_group::$Point;
+
+    #[derive(Clone, Copy, PartialEq, Eq, Debug, Zeroize)]
+    pub struct $Ciphersuite;
+    impl Ciphersuite for $Ciphersuite {
+      type F = Scalar;
+      type G = $Point;
+      type H = Sha512;
+
+      const ID: &'static [u8] = $ID;
+
+      fn generator() -> Self::G {
+        $Point::generator()
+      }
+
+      fn hash_to_F(dst: &[u8], data: &[u8]) -> Self::F {
+        Scalar::from_hash(Sha512::new_with_prefix(&[dst, data].concat()))
+      }
+    }
+  };
+}
+
+#[cfg(any(test, feature = "ristretto"))]
+dalek_curve!("ristretto", Ristretto, RistrettoPoint, b"ristretto");
+
+#[cfg(feature = "ed25519")]
+dalek_curve!("ed25519", Ed25519, EdwardsPoint, b"edwards25519");