Update derived traits, add ability to zeroize on drop, and refactor

tests/random.rs

@@ -1,5 +1,4 @@
-#![cfg(feature = "rand")]
-
+use crypto_bigint::subtle::ConstantTimeEq;
 use diffie_hellman::{Public, Secret};
 
 #[test]
@@ -13,5 +12,5 @@ fn random_dh_key_exchange() {
     let sa = a.diffie_hellman(&pb);
     let sb = b.diffie_hellman(&pa);
 
-    println!("{} == {}", sa, sb)
+    assert!(bool::from(sa.ct_eq(&sb)));
 }