Updated SubscriptionAddOnList.Add(AddOn, quantity) to pull UnitAmountInCents from the AddOn object, throwing a ValidationException when it cannot. Added tests, as well. Addresses Issue #37 on the Recurly GitHub issue tracker.
Merge pull request #43 from imerchant/issue37

Updated SubscriptionAddOnList.Add(AddOn, quantity) to address Issue #37
release 1.1.5 (stable)