Added scaffolding + TODO

CodeGenerator/BlendExt.cs

@@ -0,0 +1,9 @@
+namespace CodeGenerator;
+
+public class BlendExt {
+    //TODO: Add an bool IsPrincipal extension method to kaitai structs lib
+    //A principal (or root) block is defined by having a two digit code and by the fact that its dna_index is always valid.
+    //If we have a pointer to a principal block, we can ignore the type of the pointer and use the block type.
+    //Subsidiary blocks are defined by having the code "DATA", which is ommited here. Their dna_index is not
+    // always correct and is only used when whichever field points to them has an "invalid" type (like void*).
+}