Add missing parameters for custom collections.
Add missing parameters for custom collections.

See http://docs.shopify.com/api/customcollection for parameters.

ShopifyExtras/PHP-Shopify-API-Wrapper,kristofers91/PHP-Shopify-API-Wrapper,sebmaynard/PHP-Shopify-API-Wrapper,cargix1/PHP-Shopify-API-Wrapper