url attribute in pageCache is not used and is incorrect when the back button is used
Change cache key to be url instead of state position
Reflect url immediately upon visit. No need to call rememberCurrentUrl() on xhr.abort
Display a cached copy of a page if available before fetching its replacement
Constrain the cache size by removing the oldest caches
Add an opt-out for transition cache
Disable transition cache by default. Allow opt-in via Turbolinks.enableTransitionCache()
Add back the url attribute in pageCache