Auto merge of #67 - ebfull:static-engine, r=ebfull

Engine should always be 'static, for flexibility in downstream code.

src/bls12_381/mod.rs

@@ -21,7 +21,7 @@ use super::{Engine, CurveAffine, Field, BitIterator};
 const BLS_X: u64 = 0xd201000000010000;
 const BLS_X_IS_NEGATIVE: bool = true;
 
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 pub struct Bls12;
 
 impl Engine for Bls12 {

src/lib.rs

@@ -34,7 +34,8 @@ use std::io::{self, Read, Write};
 /// An "engine" is a collection of types (fields, elliptic curve groups, etc.)
 /// with well-defined relationships. In particular, the G1/G2 curve groups are
 /// of prime order `r`, and are equipped with a bilinear pairing function.
-pub trait Engine: Sized {
+pub trait Engine: Sized + 'static + Clone
+{
     /// This is the scalar field of the G1/G2 groups.
     type Fr: PrimeField;