Feature gate key generation on the "rand" dependency.

See https://github.com/dalek-cryptography/ed25519-dalek/pull/139.

src/keypair.rs

@@ -125,6 +125,7 @@ impl Keypair {
     /// The standard hash function used for most ed25519 libraries is SHA-512,
     /// which is available with `use sha2::Sha512` as in the example above.
     /// Other suitable hash functions include Keccak-512 and Blake2b-512.
+    #[cfg(feature = "rand")]
     pub fn generate<R>(csprng: &mut R) -> Keypair
     where
         R: CryptoRng + RngCore,

src/secret.rs

@@ -165,6 +165,7 @@ impl SecretKey {
     /// # Input
     ///
     /// A CSPRNG with a `fill_bytes()` method, e.g. `rand::OsRng`
+    #[cfg(feature = "rand")]
     pub fn generate<T>(csprng: &mut T) -> SecretKey
     where
         T: CryptoRng + RngCore,