Merge pull request #34 from NacreData/master

Fix list_subscriptions method, add tests for list_subscriptions
Provide access to customer->discount->start
Merge pull request #37 from andrewsolomon/master

Provide access to customer->discount->start
Deleting a Customer-wide Discount
Merge pull request #40 from andrewsolomon/master

Deleting a Customer-wide Discount