Group router-usable navigation api.

index.js

@@ -62,12 +62,14 @@ export default navigationStateKey => {
 
     return {
         backButtonHandler,
-        getNavigationState,
-        topOfNavigationStack,
-        resetRoutes,
-        isRoute,
-        isTopRoute,
-        goBackFrom,
+        api: {
+            getNavigationState,
+            topOfNavigationStack,
+            resetRoutes,
+            isRoute,
+            isTopRoute,
+            goBackFrom
+        },
         createConnectedNavigatorPieces
     };
 };