[WIP] Add paginator helper

Unfinished and untested. Just to get the ball rolling.
Comments and suggestions are highly welcome.

* [x] Allow to set some options
* [x] Checks if order attribute is an accepted range
* [ ] Take into account when `options[:end] > count`
* [ ] Get data from request header
* [ ] Parse request header
* [ ] Allow to set order
* [ ] Add tests