Add headings to rake routes table

Another "get some feedback on this idea" PR. Thanks @burtlo!

It's easy to forget what the order of things are in the routing table, especially if you're new. The HTML view has headings, but the console does not. They're a little different at the moment due to space, but I can change them to be as close to possible once we determine this is a good idea.

```
$ rake routes
  Prefix Verb   URI Pattern              Controller#Action
    foos GET    /foos(.:format)          foos#index
         POST   /foos(.:format)          foos#create
 new_foo GET    /foos/new(.:format)      foos#new
edit_foo GET    /foos/:id/edit(.:format) foos#edit
     foo GET    /foos/:id(.:format)      foos#show
         PATCH  /foos/:id(.:format)      foos#update
         PUT    /foos/:id(.:format)      foos#update
         DELETE /foos/:id(.:format)      foos#destroy
```

One other thing I'd like to implement, but haven't: test if we're running in a shell or not. If we're not, then we shouldn't print the headings. If you're writing scripts that rely on the output of the task, no headings is way better.