Gocardless

* Add new API attributes to resource classes:
* `BankDetailsLookup.bic`
* `Creditor.default_sek_payout_account`
* `Customer.language`
* `Customer.swedish_identity_number`
* `Event.organisation`
* `RedirectFlow.customer`
* `Refund.reference`

* Fix support for endpoints that use "data" as the request envelope
* Make exception string representations more detailed

* Update to api version 2015-07-06
* Add more detailed user agent header

Initial public release. This library is in beta until it hits 1.0, so backwards
incompatible changes may be made in minor version releases.