Introduce Ristretto signing (#1730)

* first draft of ristretto crypto module #1685

* adds better comments and code-style

* remove the last evil unwrap

* remove a mistakenly committed lockfile

* add a fresh new lockfile --will probably need a manual merge later

* fix an invalid old test vector

* Wire in ristretto

* Update comment

* Fix use.

* new Signature type api alias to be compatible with substrate

* Add new keyring, fix node executor tests

* Bump version.

* Remove all hashes.

* Update core/primitives/src/sr25519.rs

Co-Authored-By: gavofyork <github@gavwood.com>

* Revert back to Ed25519 (until JS UI is ready)

* Fix test

substrate/core/primitives/src/lib.rs

@@ -51,6 +51,8 @@ pub use hashing::{blake2_256, twox_128, twox_256};
 pub mod hexdisplay;
 #[cfg(feature = "std")]
 pub mod ed25519;
+#[cfg(feature = "std")]
+pub mod sr25519;
 
 pub mod u32_trait;