removed static calls from Item class allowing for non-static usage of…

[johanlerche]

Allowing for non-static usage of Feed, e.g.:

use LukeSnowden\GoogleShoppingFeed\Feed;

$feed = new Feed();
$feed->title('Test Feed');
$feed->link('http://example.com/');
$feed->description('Our Google Shopping Feed');

foreach( $products as $product ) {

$item = $feed->createItem();
$item->id($id);
$item->title($title);
$item->price($price);
$item->mpn($SKU);
$item->sale_price($salePrice);
$item->link($link);
$item->image_link($imageLink);
...
...

/** create a variant */
$variant = $item->variant();
$variant->size($variant::LARGE);
$variant->color('Red');

/**
 * One thing to note, if creating variants, delete the initial object after you've done,
 * Google no longer needs it!
 *
 * $item->delete();
 *
 */

}

// boolean value indicates output to browser
$feed->asRss(true);

Everything else will still work as before ;-)