organise repository a little bit

tests/compare_to_rope.sml

@@ -0,0 +1,16 @@
+structure CompareToRope =
+struct
+  local
+    fun folder ((pos, delNum, insStr), buffer, fIns, fDel) =
+      let
+        val buffer =
+          if String.size insStr > 0 then 
+            fIns (pos, insStr, buffer) else buffer
+      in
+        buffer
+      end
+  in
+    fun runTxns () =
+      Vector.foldl folder Txn.empty Txn.txns
+  end
+end