WooCommerce Smart Coupons 8.22.0

* New: WooCommerce 3.8.1 compatible
* Fix: Variable gift certificate product price not displaying in product description when variation is not discounted and 'Sell store credit at less price' is enabled

* New: Restrict Coupons by Product Attributes
* New: Setting to change endpoint for Coupons. The endpoint will appear in the URL when the customer is on My Account > Coupons page
* Fix: Emails not getting sent in some cases
* Fix: Email template override not working
* Fix: JavaScript error: Undefined 'woocommerce_admin_meta_boxes_coupon'
* Fix: Incorrect email preview layout under WooCommerce > Coupons > Send Store Credit tab
* Fix: Replacing usage of 'wc_selected' function with 'selected' function for better backward compatibility
* Update: Documentation links
* Update: POT file

* New: Move coupon emails in the WooCommerce email system for better handling
* New: Plain text emails for coupons
* Fix: Coupon actions not working in case of fixed amount gift voucher products
* Fix: Unable to empty coupon expiry time
* Developer: Filter 'wc_sc_calculate_totals_stop_at' to handle discount calculation for store credit
* Update: POT file