♻️ Begins to refactor for media

For #4

tests/MediaTest.php

@@ -0,0 +1,18 @@
+<?php
+
+use PHPUnit\Framework\TestCase;
+use Shikiryu\SRSS\SRSS;
+
+class MediaTest extends TestCase
+{
+    public function testImages()
+    {
+        $rss = SRSS::read('resources/media/cnn.xml');
+        self::assertEquals('CNN.com - RSS Channel - Entertainment', $rss->title);
+
+        $first_item = $rss->getFirst();
+        self::assertEquals('Kirstie Alley, \'Cheers\' and \'Veronica\'s Closet\' star, dead at 71', $first_item->title);
+
+        self::assertEquals('https://cdn.cnn.com/cnnnext/dam/assets/221205172141-kirstie-alley-2005-super-169.jpg', $first_item->{'media:group'}->{'media:content'}->url);
+    }
+}