Fix the documentation for APIExtraDataAccessHook.
Review Request #978 — Created Nov. 23, 2017 and updated
The documentation for `APIExtraDataAccessHook` had some bad references, syntax errors, and examples that didn't depict the actual usage of the hook. The inline code docs for the hook also showed the wrong usage. This fixes up all the docs to reflect the real usage of the hook and to clean up the errors so that everything is presented and linked correctly. Testing Done: Built the docs. Checked all links and checked that rendering issues were fixed. Reviewed at https://reviews.reviewboard.org/r/9382/