create VmcExtOpt and add to marionette

Marionette.cs

@@ -113,6 +113,9 @@ namespace godotVmcSharp
                 case "/VMC/Ext/Remote":
                     new VmcExtRemote(m);
                     break;
+                case "/VMC/Ext/Opt"
+                    new VmcExtOpt(m);
+                    break;
             }
         }
     }

VmcMessages/VmcExtOpt.cs

@@ -0,0 +1,43 @@
+/*
+    godotVmcSharp
+    Copyright (C) 2023  Cassandra de la Cruz-Munoz
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as published
+    by the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Affero General Public License for more details.
+
+    You should have received a copy of the GNU Affero General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+    */
+
+using Godot;
+using godotOscSharp;
+
+namespace godotVmcSharp
+{
+    public class VmcExtOpt : VmcMessage
+    {
+        public string option { get; }
+
+        public VmcExtOpt(godotOscSharp.OscMessage m) : base(m.Address)
+        {
+            if (m.Data.Count != 1)
+            {
+                GD.Print($"Invalid number of arguments for {addr}. Expecting 1, received {m.Data.Count}");
+                return;
+            }
+            if (m.Data[0].Type != 's')
+            {
+                GD.Print(InvalidArgumentType.GetErrorString(addr, "option", 's', m.Data[0].Type));
+                return;
+            }
+            option = (string)m.Data[0].Value;
+        }
+    }
+}