Move Jubjub and Pedersen hash gadgets into zcash_proofs

These are currently too Zcash-specific to be generalized, and need some
targeted refactoring.

zcash_proofs/src/circuit.rs

@@ -1,2 +1,5 @@
+pub mod ecc;
+pub mod pedersen_hash;
+
 pub mod sapling;
 pub mod sprout;