consensus: move redjubjub to new primitives module

This will let it sit alongside a groth16 verifier.

zebra-consensus/src/lib.rs

@@ -20,6 +20,6 @@ pub mod chain;
 pub mod checkpoint;
 pub mod mempool;
 pub mod parameters;
-pub mod redjubjub;
+mod primitives;
 mod script;
 mod transaction;

zebra-consensus/src/primitives.rs

@@ -0,0 +1,3 @@
+//! Asynchronous verification of cryptographic primitives.
+
+pub mod redjubjub;