Update to new benchmarking framework (#126)

bn254/benches/bn254.rs

@@ -0,0 +1,13 @@
+use ark_algebra_bench_templates::*;
+use ark_bn254::{fq::Fq, fq2::Fq2, fr::Fr, Bn254, Fq12, G1Projective as G1, G2Projective as G2};
+
+bench!(
+    Name = "BN254",
+    Pairing = Bn254,
+    G1 = G1,
+    G2 = G2,
+    ScalarField = Fr,
+    G1BaseField = Fq,
+    G2BaseField = Fq2,
+    TargetField = Fq12,
+);