Picturefill method from plugin

gistfile1.html

Output the picturefill HTML, so you don't have to repeat it all over the templates.
- Param: big_img, src for big image
- Param: small_img, src for small image
- Param: alt, alt attribute for image
- Param: media_query, media query to use, defaults to (min-width: 600px)
- Param: class, class for wrapper, defaults to hero

Example Usage:
{exp:vl:picturefill
	big_img="{custom_field_name}"
	small_img="{exp:ce_img:pair src='{custom_field_name}' width='600'}{made}{/exp:ce_img:pair}"
}

pl.plugin.php

/**
 * Picturefill Helper
 *
 * @return string with picturefill output
 */
public function picturefill()
{

	$big_img = $this->EE->TMPL->fetch_param('big_img', NULL);
	$small_img = $this->EE->TMPL->fetch_param('small_img', NULL);
	$alt = $this->EE->TMPL->fetch_param('alt', NULL);
	$media_query = $this->EE->TMPL->fetch_param('media_query', '(min-width: 600px)');
	$class = $this->EE->TMPL->fetch_param('class', 'hero');
	$return_data = '';

	if($big_img && $small_img && $media_query) {
		$return_data = '<div class="' . $class . '" data-picture data-alt="' . $alt . '">
							<div data-src="' . $small_img . '"></div>
							<div data-src="' . $big_img . '" data-media="' . $media_query . '"></div>

							<!--[if (lt IE 9) & (!IEMobile)]>
								<div data-src="' . $big_img . '"></div>
							<![endif]-->

							<!-- Fallback content for non-JS browsers. Same img src as the initial, unqualified source element. -->
							<noscript>
								<img src="' . $small_img . '" alt="' . $alt . '">
							</noscript>
						</div>';
	}

	return $return_data;
}