Update links to Rest API docs

[marians]

Two benefits:

• No redirect needed, users land on the final URL immediately.
• This will make maintenance easier, as it will be easier to find internal links that do not use the relref shortcode.

[AndiDog]

That's really outdated REST API stuff, maybe leave it or remove it?

[marians]

There is a reason to do this

This will make maintenance easier, as it will be easier to find internal links that do not use the relref shortcode.