Implements Signer generic for validator client and epoch duties

eth2/utils/bls/src/keypair.rs

@@ -1,5 +1,6 @@
 use super::{PublicKey, SecretKey};
 use serde_derive::{Deserialize, Serialize};
+use std::fmt;
 use std::hash::{Hash, Hasher};
 
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
@@ -32,3 +33,9 @@ impl Hash for Keypair {
         self.pk.as_uncompressed_bytes().hash(state)
     }
 }
+
+impl fmt::Display for Keypair {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.pk)
+    }
+}