Use variadic parameters

Author: ikesyo

Sources/Commandant/Command.swift

@@ -91,11 +91,13 @@ public final class CommandRegistry<ClientError: Error> {
 	/// If another command was already registered with the same `verb`, it will
 	/// be overwritten.
 	@discardableResult
-	public func register<C: CommandProtocol>(_ command: C)
+	public func register<C: CommandProtocol>(_ commands: C...)
 		-> CommandRegistry
 		where C.ClientError == ClientError, C.Options.ClientError == ClientError
 	{
-		commandsByVerb[command.verb] = CommandWrapper(command)
+		for command in commands {
+			commandsByVerb[command.verb] = CommandWrapper(command)
+		}
 		return self
 	}