Adding AdditiveGroup and PrimeGroup (#159)

Co-authored-by: Michele Orrù <michele.orru@berkeley.edu>
Co-authored-by: Weikeng Chen <w.k@berkeley.edu>
Co-authored-by: Pratyush Mishra <pratyushmishra@berkeley.edu>

vesta/src/curves/mod.rs

@@ -3,7 +3,7 @@ use ark_ec::{
     models::CurveConfig,
     short_weierstrass::{self as sw, SWCurveConfig},
 };
-use ark_ff::{Field, MontFp, Zero};
+use ark_ff::{AdditiveGroup, Field, MontFp, Zero};
 
 #[cfg(test)]
 mod tests;