Add additional interface; remove fulfill endpoint
Rename sku to item
Rename a few spec files
Rename confirmation_code to actv_code
Add additional validation to Order class
Add or remove order only when purchase is created and pending
Set amount on saving order
Bug fix; better interface
Add pry
Add GBP currency unit
Add currency exchange table
Initialize the exchange rates
Add rate exchage method to Currency model
Add tax rates to orders
Add currency to payment method model
Set tax, tax rates, and amount properly
Aggregate amount and tax of all orders for purchase, given a currency
Allow Purchase#add_order to change currency and quantity
Change submitted to committed
Add Committable and CommittableScope interfaces