Sassafras primitives (#1249)

* Introduce Sassafras primitives

* Keystore workaround

* Fix doc

* Use  in keystore

* Improve bandersnatch vrf docs

* Apply review suggestions

* Update README

* Docs improvement

* Docs fix

substrate/primitives/keystore/src/lib.rs

@@ -17,6 +17,7 @@
 
 //! Keystore traits
 
+#[cfg(feature = "std")]
 pub mod testing;
 
 #[cfg(feature = "bandersnatch-experimental")]
@@ -631,3 +632,15 @@ impl KeystoreExt {
 		Self(Arc::new(keystore))
 	}
 }
+
+sp_core::generate_feature_enabled_macro!(
+	bandersnatch_experimental_enabled,
+	feature = "bandersnatch-experimental",
+	$
+);
+
+sp_core::generate_feature_enabled_macro!(
+	bls_experimental_enabled,
+	feature = "bls-experimental",
+	$
+);