feat(router): add support for custom route reuse strategies

modules/@angular/router/src/index.ts

@@ -12,6 +12,7 @@ export {RouterLink, RouterLinkWithHref} from './directives/router_link';
 export {RouterLinkActive} from './directives/router_link_active';
 export {RouterOutlet} from './directives/router_outlet';
 export {CanActivate, CanActivateChild, CanDeactivate, CanLoad, Resolve} from './interfaces';
+export {DetachedRouteHandle, RouteReuseStrategy} from './route_reuse_strategy';
 export {Event, NavigationCancel, NavigationEnd, NavigationError, NavigationExtras, NavigationStart, Router, RoutesRecognized} from './router';
 export {ExtraOptions, ROUTER_CONFIGURATION, ROUTER_INITIALIZER, RouterModule, provideRoutes} from './router_module';
 export {RouterOutletMap} from './router_outlet_map';