Add Grumpkin support for arkworks (#174)

Co-authored-by: Pratyush Mishra <pratyushmishra@berkeley.edu>

grumpkin/benches/grumpkin.rs

@@ -0,0 +1,9 @@
+use ark_algebra_bench_templates::*;
+use ark_grumpkin::{fq::Fq, fr::Fr, Projective as G};
+
+bench!(
+    Name = "Grumpkin",
+    Group = G,
+    ScalarField = Fr,
+    PrimeBaseField = Fq,
+);