Add route collector to ApiTaster

Currently `ApiTaster.routes` could be called only once, for example if
we will call this code, the only last rule will be applyed.

```ruby
ApiTaster.routes do
  get '/posts'
end

ApiTaster.routes do
   get '/posts/:post_id/comments'
end
```

We need to store routes in to `app/api_tasters/**/*` and have ability to load them one by one.
Here is how to implement it https://gist.github.com/timurvafin/5082251