begin merging files which were previously in temp-squares directory into main

fcore/app-update.sml

@@ -0,0 +1,9 @@
+structure AppUpdate =
+struct
+  open AppType
+
+  fun update (model: app_type, inputMsg) =
+    case #mode model of
+      NORMAL_MODE => NormalMode.update (model, inputMsg)
+    | BROWSE_MODE => BrowseMode.update (model, inputMsg)
+end