Profile support for links

[dblock]

Porting from TODO.

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@oriolgual I blindly copied this from the TODO, can you please explain what it means? :)

[oriolgual]

Yup, is something defined at the HAL specs: https://tools.ietf.org/html/draft-kelly-json-hal-06#section-7.1 (see also https://tools.ietf.org/html/draft-wilde-profile-link-04)

TLDR: A link that has some kind of description/documentation about how to use that resource.