Image lazy loading - tag attribute added

Lazy image loading is supported by all current browsers per attribute. Devices that do not recognise this attribute actually ignore it.

https://caniuse.com/?search=loading%3D%22lazy%22

Parsedown.php

@@ -1373,6 +1373,7 @@ protected function inlineImage($Excerpt)
                 'attributes' => array(
                     'src' => $Link['element']['attributes']['href'],
                     'alt' => $Link['element']['handler']['argument'],
+                    'loading' => 'lazy',
                 ),
                 'autobreak' => true,
             ),