Fix: Check if cart is set before trying to access cart_contents.
Fix: Use native functions to get parent container versus searching cart directly.
Tweak: Add product_id as data attribute to add to cart button, to help some themes that add ajax add to cart.
Tweak: Auto load certain properties if not defined.
Tweak: Instead of resetting to minium quantity value, set to original value attribute.
Tweak: Add broader support for checkbox/dropdown input types.