Discover Authorship

Since this repo is still used by a lot of sites, better to actually file issues :)

It seems like php-comments does not follow the algorithm for discovering authorship as described on https://indieweb.org/authorship
Some chat around it: https://chat.indieweb.org/dev/2017-01-02#t1483370937764000

Few challenges with this:

1. `parse()` takes a `h-` object. You pass in the `$mf2['items']` part that comes out of a Mf2 parser, not the whole thing. This means you have no access to the `$mf2['rels']` part of the page, where `rel="author"`-links reside.

2. When the author is only a URL, (step 7) we need to grab another page. Currently, there is no curling nor mf2 parsing done inside of php-comments, so that's impossible.

@aaronpk's [XRay](https://github.com/aaronpk/XRay) does a better job at these things.

Start at parse(), which receives the h- object from the Mf2 parser, and compare its inputs with the authorship algorithm on indieweb.org. Review how the missing $mf2['rels'] data affects rel="author" links, then examine the URL-only author step and XRay's behavior as a reference. Done means the required authorship cases can be handled, including fetching and parsing another page.

Written by the indexing model from the issue text.