Tweaks to links in API results / docs

[PhantomWatson]

• [ ] /categories results need a $category['links']['events'] value (i.e. /v1/events/category/{categoryId})
• [ ] All $foo['links'] results need to be documented (if intended) or removed from results (if not)
• [x] 'self' link is documented, but not in results (at least not in /event/{eventID} results)
• [ ] Unneeded pagination links in /event endpoint need removed