Add Classic/Compromise DLEqs and a benchmark

Formatted results from my laptop:

EfficientLinear had a average prove time of 188ms
EfficientLinear had a average verify time of 126ms

CompromiseLinear had a average prove time of 176ms
CompromiseLinear had a average verify time of 141ms

ConciseLinear had a average prove time of 191ms
ConciseLinear had a average verify time of 160ms

ClassicLinear had a average prove time of 214ms
ClassicLinear had a average verify time of 159ms

There is a decent error margin here. Concise is a drop-in replacement 
for Classic, in practice *not* theory. Efficient is optimal for 
performance, yet largest. Compromise is a middleground.

crypto/multiexp/src/tests/mod.rs

@@ -96,8 +96,8 @@ fn test_ed25519() {
   test_multiexp::<EdwardsPoint>();
 }
 
-#[test]
 #[ignore]
+#[test]
 fn benchmark() {
   // Activate the processor's boost clock
   for _ in 0 .. 30 {