Simple, leveraging default options

Works as of commit 3ff70d6926.

use GuzzleHttp\Psr7;
use SimplePie\SimplePie;

// Instantiate SimplePie.
$simplepie = new SimplePie();

// Pass a PSR-7 stream to SimplePie for parsing.
$stream = Psr7\stream_for(file_get_contents(__DIR__ . '/releases.atom'));

// Specifically parses XML.
$parser = $simplepie->parseXml($stream, true);

// Reference the top-level feed object
$feed = $parser->getFeed();

// Use familiar syntax to read the data you care about.
echo $feed->getTitle();
foreach ($feed->getItems() as $item) {
    echo $item->getTitle();
}