Add the secp256k1 and secq256k1 curves (#122)

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

secp256k1/src/fields/fr.rs

@@ -0,0 +1,7 @@
+use ark_ff::fields::{Fp256, MontBackend, MontConfig};
+
+#[derive(MontConfig)]
+#[modulus = "115792089237316195423570985008687907852837564279074904382605163141518161494337"]
+#[generator = "7"]
+pub struct FrConfig;
+pub type Fr = Fp256<MontBackend<FrConfig, 4>>;