Support route chaining: return this when adding a route

When setting up routes you currently have to do separate route additions via:

``` coffee
Finch.route '/', ->
  console.log 'home'
Finch.route '/about', ->
  console.log 'about'
```

This might seem fine when using this in coffeescript, but for those of us that use straight javascript it becomes this:

``` js
Finch.route('/', function () {
  console.log('home');
});
Finch.route('/about', function () {
  console.log('about');
});
```

By returning the 'this' object you allow the pure javascript to look like this:

``` js
Finch
  .route('/', function () {
    console.log('home');
  })
  .route('/about', function () {
    console.log('about');
  });
```

Which we prefer.