add functionality to move between start button/options button

fcore/title/title-update.sml

@@ -9,8 +9,35 @@ struct
           val mode =
             if #attackHeld input orelse #jumpHeld input then
               GameType.LEVEL LevelType.initial
-            else
+            else 
+              let
+                val titleState =
+                  if #downHeld input then
+                    {focus = OPTIONS_BUTTON}
+                  else
+                    titleState
+              in
+                GameType.TITLE titleState
+              end
+        in
+          {mode = mode, userKeys = userKeys}
+        end
+    | OPTIONS_BUTTON =>
+        let
+          val mode = 
+            if #attackHeld input orelse #jumpHeld input then
+              (* placeholder: go to configure screen instead once that is implemented *)
               GameType.TITLE titleState
+            else
+              let
+                val titleState =
+                  if #upHeld input then
+                    {focus = START_BUTTON}
+                  else
+                    titleState
+              in
+                GameType.TITLE titleState
+              end
         in
           {mode = mode, userKeys = userKeys}
         end