Add OPTS command

DearFTP/Connection/Commands/CommandsDispatcher.cs

@@ -18,6 +18,7 @@ namespace DearFTP.Connection.Commands
             new ListCommand(),
             new ListMachineCommand(),
             new MakeDirectoryCommand(),
+            new OptionsCommand(),
             new ParentDirectoryCommand(),
             new PassiveCommand(),
             new PwdCommand(),

DearFTP/Connection/Commands/OptionsCommand.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace DearFTP.Connection.Commands
+{
+    class OptionsCommand : ICommand
+    {
+        public string[] Aliases { get; } = new string[]
+        {
+            "OPTS"
+        };
+
+        public void Execute(Session session, FtpStream stream, string alias, string argument)
+        {
+            if (argument.ToUpper().Contains("UTF"))
+            {
+                stream.Send(ResponseCode.OK, "UTF8 supported on this server.");
+                return;
+            }
+
+            stream.Send(ResponseCode.ArgumentsError, "Requested option not supported");
+        }
+    }
+}