Cursor-based pagination

Facebook introduced new cursor based pagination https://developers.facebook.com/docs/reference/api/pagination/.

Due to July 2013 Breaking Changes in Facebook, old pagination, based on offset, stopped to work. I think, the solution is very similar to recent commit about supporting __after_id and __before_id. 

They are return similar code in response:
```
  "paging": {
    "cursors": {
      "after": "MjU=", 
      "before": "MQ=="
    }, 
    "next": "https://graph.facebook.com/post_id/comments?filter=stream&limit=25&after=MjU="
  }
```