add_to_cart() return $cart_item_key
re-add v1 API classes
implement separate handlers for v1/v2 REST API requests
update get_woocommerce_api_url() to handle multiple versions
API: implement order deletion

part of #4160
set a proper code for wp_error
API: implement order creation

part of #4160
fixing typos in abstract settings class
Put the whole coupon message in the filter.
Add filter: wc_get_template

Allow 3rd party plugin filter template file from their plugin
Merge pull request #5851 from BFTrick/abstract-settings-typos

Fixing Typos in Abstract Settings Class
Merge pull request #5858 from woothemes/filter-whole-coupon-message

Put the whole coupon message in the filter.
Merge pull request #5872 from Ninos/master

Add filter: wc_get_template
update docblock for add_to_cart() method
Merge pull request #5822 from helgatheviking/fix/add-to-cart

add_to_cart() return $cart_item_key
Add WC_API_Exception class

Part of #4160
Add wc_update_order_item() function
Fix misc docblocks
Add update methods to WC_Abstract_Order

These methods compliment the existing add_*() methods and provide a
consistent interface to add and update items for the order.

Part of #4160
Add calculate_shipping() method to WC_Abstract_order

When the update_shipping() method is used, the order shipping amount is
not properly calculated unless the shipping costs are summed.

Part of #4160