Crypto fixes/improvements (#2008)

* Crypto fixes:

- Use schnorrkel's HDKD derive
- Assume all key URIs beginning with `/` are prefixed with public
  root phrase.

* Remove commented code.

* Update README

* Update core/primitives/src/ed25519.rs

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

substrate/core/cli/src/lib.rs

@@ -63,9 +63,6 @@ use substrate_telemetry::TelemetryEndpoints;
 
 const MAX_NODE_NAME_LENGTH: usize = 32;
 
-/// The root phrase for our development network keys.
-pub const DEV_PHRASE: &str = "bottom drive obey lake curtain smoke basket hold race lonely fit walk";
-
 /// Executable version. Used to pass version information from the root crate.
 pub struct VersionInfo {
 	/// Implemtation name.
@@ -390,7 +387,7 @@ where
 	}
 
 	if cli.shared_params.dev {
-		config.keys.push(format!("{}//Alice", DEV_PHRASE));
+		config.keys.push("//Alice".into());
 	}
 
 	let rpc_interface: &str = if cli.rpc_external { "0.0.0.0" } else { "127.0.0.1" };