allows the XKCD XML feeds to be parsed with the feed parser

using fork of picofeed with 0.1.38 tag on aaronpk repo

the zend security model runs libxml_disable_entity_loader to disable it so it's fine to allow

* adds test of instagram-atom feed with individual authors per item
* dedupes atom/rss title if it's a prefix of the content

if an item has multiple URL values, return the one that is on the same domain

# Conflicts:
#	README.md
#	composer.json
#	composer.lock

includes info on feed parsing

Treats `https://example.com` and `https://example.com/` as equivalent when comparing URLs. Closes #33

closes #32

uses the video's poster frame as the photo if any of the multi-post images are videos

according to http://microformats.org/wiki/h-entry the rsvp values should be interpreted case-insensitive

checkin data is returned embedded like author data rather than in the `refs` object

closes #35

closes #40

thanks to the new backcompat in php-mf2 0.3.2

Refactors into a library that can be used separately from the API