v2.0: Adding additional mime types for downloadable files, to improve handling on iOS devices in particular.
v2.0: Adding additional values to the shipping custom code and custom endpoint payloads.
API: Updates to payment_method_uri on cart resources, to allow for better handling of previous non-Stripe credit card transactions to use Stripe for current/future transactions.
API: Fixing an unclear error and edge case bug where an API-created cart would complete a transaction for subscription with a guest customer.
ALL VERSIONS: Removing legacy crossdomain.xml file.