Optimizations (#100)

* avoid creating commitments to zero vectors

* reduce the number of constraints in each iteration from 4 to 3

src/traits/mod.rs

@@ -64,6 +64,12 @@ pub trait Group:
 
   /// Returns the order of the group as a big integer
   fn get_order() -> BigInt;
+
+  /// Returns an element that is the additive identity of the group
+  fn zero() -> Self;
+
+  /// Returns the generator of the group
+  fn get_generator() -> Self;
 }
 
 /// Represents a compressed version of a group element