fix: check prefix correctly

The test is checking for notes, but 'Bridge Fed' is, in fact, an article according to the post discovery algorithm. Also, I'm adding as note that the main difference between a note and an article is that the latter has a title, while the first doesn't.

`strpos(string, sub)` returns `false` if `sub` is not present in `string`. In this case, we want to check if `sub` is not a *prefix* of `string`. Hence, we just need to test if the returned position is simply different from 0.

* looks through the full mf2 tree for step 7 of authorship https://github.com/indieweb/authorship/issues/2
* if no author h-card is found, falls back to returning the author URL without other data instead of missing author

closes #95

Allow iframe from YouTube and Vimeo

need to update htmlpurifier first

if the document contains a link to the target, but that link is not in the parsed result, don't return an error, but also don't return the parsed document

closes #150

for https://github.com/aaronpk/webmention.io/issues/150

closes #96

XRay now looks for images inside the HTML and does not consider those empty posts

Add support for parsing MF2 JSON

To make it possible to consume feeds of pre-rendered Microformats2 JSON
data, we need to be able to discover that it is a Microformats2 JSON
file using the known MIME types documented  in
http://microformats.org/wiki/microformats2-mime-type

move target check outside of all format classes and operating on the final parsed JSON so that it works regardless of the input content type

for https://github.com/aaronpk/Aperture/issues/56

closes #89

closes #92

we also need the controller files!