Fix   - Missing CSS and JS assets causing broken styles and functionality.

* Tweak - Refactor address validation

* Fix   - Fatal error with custom billing fields added from 'woocommerce_checkout_fields' filter hook.

* Tweak - Use order CRUD classes to save or get meta data.

* Fix   - Editing address in admin does not support custom address fields.

* Tweak - Remove the empty recipient-form.php file.

* Fix   - Different subtotal, tax, and discount value when one cart item has multiple addresses.

* Fix   - Incorrect shipping method in the order.

* Fix   - Overlap select field in address form.

* Fix   - Different subtotal value when discount coupon is used.

* Fix   - "Undefined Index: price" notice error when using WC Composite Product plugin.

* Fix   - Address array is missing in package destination.

* Fix   - "Set Multiple Address" button to always show regardless of cart item quantity.

* Fix   - Shipping methods always display "(incl. tax)" text regardless of tax display settings.

* Add   - Save billing address fields functionality when click "Set Multiple Address" button.

* Tweak - Move the location of the "Set Multiple Address" button to shipping address area.

* Tweak - Simplify duplicate cart process.

* Fix   - Taxes added even when customer is tax exempt.

* Tweak - Refactor the code for add ons compatibility.

* Fix   - Use subtotal for free shipping calculation.

* Fix   - Add new address button does not work in plain or numeric permalink.

* Fix   - Display multiple addresses in preview order.