make edwards an optional feature, and separate benches

src/edwards.rs

@@ -1,3 +1,5 @@
+#![cfg(feature = "edwards")]
+
 use crate::traits::{Curve, Point};
 use crypto_bigint::{AddMod, ConstZero, Integer, InvMod, MulMod, NonZero, SubMod, U448};
 use std::ops::Div;

src/lib.rs

@@ -1,6 +1,7 @@
 #[macro_use]
 mod macros;
 
+#[cfg(feature = "edwards")]
 pub mod edwards;
 pub mod montgomery;
 pub mod traits;