removed single subscription entity in place of multiple subscriptions (https://stripe.com/docs/upgrades?since=2013-12-03#2014-01-31). also delinquent on customer is not nullable.
updated statement descriptor to statement description per stripe api changes
updated all of the list methods to support valid properties on the new stripe api
updated readme to reflect new changes
changed amountInCents to be amount everywhere (no longer relevant to just US)
bumped to 2.0.0