Retina images using srcset attribute

Add Retina and Responsive images using the srcset attribute in the image tag.

Basic Usage

<img src="image.jpg" srcset="image@2x.jpg 2x" alt="" />

WordPress Logo Usage

<a href="<?php bloginfo('url'); ?>">
<img src="<?php bloginfo('template_directory'); ?>/_assets/img/logo.png" srcset="<?php bloginfo('template_directory'); ?>/_assets/img/logo@2x.png 2x" alt="<?php bloginfo('name'); ?>" />
</a>

Advanced Usage

<img srcset="image-320w.jpg 320w,
             image-480w.jpg 480w,
             image-800w.jpg 800w"
     sizes="(max-width: 320px) 280px,
            (max-width: 480px) 440px,
            800px"
     src="image-800w.jpg" alt="">