encapsulate template logic

mROA.Codegen/TemplateDocumentExtensions.cs

@@ -0,0 +1,16 @@
+using System;
+using mROA.CodegenTools;
+
+namespace mROA.Codegen
+{
+    public static class TemplateDocumentExtensions
+    {
+        public static TemplateDocument CloneInnerTemplate(this TemplateDocument template, string tag)
+        {
+            var innerTemplate = template[tag] as InnerTemplateSection 
+                                ?? throw new InvalidOperationException();
+            var clone = innerTemplate.InnerTemplate.Clone();
+            return (TemplateDocument)clone;
+        }
+    }
+}