Gravity Perks - eCommerce Fields 1.2.28

Added support for using choice values in order summary: {order_summary:value}.

Fixed issue where product-specific discounts were incorrectly calculated when the product total was 0.
Fixed issue where {subtotal} merge tag replacement was inaccurate when multiple Calculation Product fields contained a {subtotal} merge tag.

Fixed order-of-events issue where calculations containing the {coupons} were recalculated prematurely.