Added convertible interface

Author: vpenades

src/SharpGLTF.Core/Schema2/IConvertibleToGltf2.cs

@@ -0,0 +1,14 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace SharpGLTF.Schema2
+{
+    /// <summary>
+    /// Defines a method that converts the implementing reference to a <see cref="ModelRoot"/>
+    /// </summary>
+    public interface IConvertibleToGltf2
+    {
+        ModelRoot ToGltf2();
+    }
+}