Coupon system

This module is currently under design stage. For your information I've included a summary of module purposes.

A coupon is a digital representation of the right to claim goods, promotion or services. The usage of coupons is defined as "voucher". To clarify workflow and terminology, let I be a voucher issuer, H be a voucher holder, P be the issuer's 'promise' to the voucher holder. A voucher is defined as the 3-tuple of [ I (issuer), P (promise), H (holder) ].

Examples of P (Promises) are as follows:
o 100 loyalty points are added to the card per purchase: Loyalty points
o Take 10% off your total purchase by using a "card ID": Membership card
o Take 50% off your total purchase with a coupon: Discount coupon
o The bearer can access "http://..." for one month free: Free ticket for sales promotion
o The bearer can exchange a ticket for the ordered goods: Exchange ticket or delivery note
o The bearer can create content in the site: services coupon
o Seat number A-24 has been reserved for "a-concert" on April 2: Event ticket

This module will not do anything by itself, and sould only be installed if other modules require you to do.