Async err-thang

Every callback should be asynchronous.

The code may look something like:

``` js
Promise.resolve(newRoute.beforeFetch(routeData))
.then(Promise.resolve(newRoute.fetch(routeData))
.then(Promise.resolve(newRoute.afterFetch(routeData))
.then( /* current logic */ )
```

Whether or not there should be asynchronous exits for routes will depend on how I want animated exits to work.

Start by locating the route callback flow involving beforeFetch, fetch, and afterFetch, then inspect how the current logic handles these callbacks. Determine the intended asynchronous sequencing and whether route exits are included, since the issue leaves animated exits unresolved. Done means the callback behavior and exit scope are defined and implemented consistently.

Written by the indexing model from the issue text.