Add benchmarks

CliFx.Benchmarks/Commands/SystemCommandLineCommand.cs

@@ -0,0 +1,34 @@
+using System.CommandLine;
+using System.CommandLine.Invocation;
+using System.Threading.Tasks;
+
+namespace CliFx.Benchmarks.Commands
+{
+    public class SystemCommandLineCommand
+    {
+        public static int ExecuteHandler(string s, int i, bool b) => 0;
+
+        public Task<int> ExecuteAsync(string[] args)
+        {
+            var command = new RootCommand
+            {
+                new Option(new[] {"--str", "-s"})
+                {
+                    Argument = new Argument<string>()
+                },
+                new Option(new[] {"--int", "-i"})
+                {
+                    Argument = new Argument<int>()
+                },
+                new Option(new[] {"--bool", "-b"})
+                {
+                    Argument = new Argument<bool>()
+                }
+            };
+
+            command.Handler = CommandHandler.Create(typeof(SystemCommandLineCommand).GetMethod(nameof(ExecuteHandler)));
+
+            return command.InvokeAsync(args);
+        }
+    }
+}