Small improvements to the Cookbook page

[regisrob]

A small suggestion for the Cookbook page: enable the ability to point someone to a particular section of the Cookbook with a URL. E.g. "here the list of cookbook recipes about annotations you might be interest in: https://iiif.io/api/cookbook/#other-kinds-of-annotations". So it may be useful to add anchor navigation/linking as it is the case in the API pages (small link icon which appears on hover, and maybe a clickable ToC as well at the top under "The Recipes"?)