Pagination links should not go directly in links object

[jpadilla]

According to the spec, pagination keys first, last, prev, and next should in the links object. This library currently forces you to add them in links.pagination. I can get a PR together if we agree.

Pagination links MUST appear in the links object that corresponds to a collection. To paginate the primary data, supply pagination links in the top-level links object. To paginate an included collection returned in a compound document, supply pagination links in the corresponding links object.

The following keys MUST be used for pagination links:

• first: the first page of data
• last: the last page of data
• prev: the previous page of data
• next: the next page of data

[digia]

It should be inline with the spec. I've been adding things as i run into them on my project.

A PR for this would be greatly appreciated.

Thank you!