Add hook for attaching extra custom data to different json endpoints

[TylerBarnes]

The hook should just be something like add_wordsby_collections_data or something like that.
It should pass in the ID of the current post as it loops through all posts and an array of named arrays should be returned.

There should be a hook to add data to the following files

• collections.json
• users.json (once this is added)
• menus.json
• options.json
• sitemeta.json