Make relay CLI generic (#849)

* Start generalizing rialto-millau commands.

* cargo fmt --all

* Introduce generic balance.

* Unify message payloads.

* cargo fmt --all

* init - generic

* Attempt to unify send message.

* Start moving things around.

* cargo fmt --all

* Move init-bridge.

* cargo fmt --all

* Improve UX of bridge argument.

* Fix clippy.

* Fix docs and scripts.

* Add docs.

* Apply suggestions from code review

Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>

* Fix copyright.

* Add issue numbers.

* More todos.

* Update comments.

Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>

bridges/relays/client-substrate/src/error.rs

@@ -42,6 +42,19 @@ pub enum Error {
 	Custom(String),
 }
 
+impl std::error::Error for Error {
+	fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+		match self {
+			Self::RpcError(ref e) => Some(e),
+			Self::ResponseParseFailed(ref e) => Some(e),
+			Self::UninitializedBridgePallet => None,
+			Self::AccountDoesNotExist => None,
+			Self::ClientNotSynced(_) => None,
+			Self::Custom(_) => None,
+		}
+	}
+}
+
 impl From<RpcError> for Error {
 	fn from(error: RpcError) -> Self {
 		Error::RpcError(error)
@@ -61,21 +74,23 @@ impl MaybeConnectionError for Error {
 	}
 }
 
-impl From<Error> for String {
-	fn from(error: Error) -> String {
-		error.to_string()
-	}
-}
-
-impl ToString for Error {
-	fn to_string(&self) -> String {
-		match self {
+impl std::fmt::Display for Error {
+	fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+		let s = match self {
 			Self::RpcError(e) => e.to_string(),
 			Self::ResponseParseFailed(e) => e.to_string(),
 			Self::UninitializedBridgePallet => "The Substrate bridge pallet has not been initialized yet.".into(),
 			Self::AccountDoesNotExist => "Account does not exist on the chain".into(),
 			Self::ClientNotSynced(health) => format!("Substrate client is not synced: {}", health),
 			Self::Custom(e) => e.clone(),
-		}
+		};
+
+		write!(f, "{}", s)
+	}
+}
+
+impl From<Error> for String {
+	fn from(error: Error) -> String {
+		error.to_string()
 	}
 }