Handle array of Link Objects

Hi,

The [spec states](http://tools.ietf.org/html/draft-kelly-json-hal-05#section-4.1.1), regarding the `_links` property:
> It is an object whose property names are link relation types (as
   defined by [RFC5988]) and values are either a Link Object or an array
   of Link Objects.

And we needed that for CURIEs, so with @julienXX we implemented it.

Enjoy,
Étienne & Julien