Add ability to add multiple instances of a dependency model

This release adds the functionality that allows you to for example att multiple products to an order. Rather than just 1 instance, which was the case before when it just to the last instance available in the fixtures array. Now it checks whether there are multiple instances available and if so does the builder allow for adding multiple instances, if both checks return true then it will add all instances available on the array of the same type.

This allows for:

$products = Factory::times(3)->make('catalog/product);
$order = Factory::with($products)->make('sales/quote);

... and so now the order will contain all three of those created products.