Update examples to use single objects instead of arrays

This replaces arrays with a single object as defined in https://github.com/json-api/json-api/pull/237

I'm not sure, but on the front page it might look better to leave the array and add a second post.. 
@BRMatt you are definitely right here

What got me confused is that on the front page it's not obvious what is being fetched, a resource or a collection