Added a refund and cancel endpoint
Merge pull request #20 from gocardless/refund-and-cancel

Added a refund and cancel endpoint
Merge branch 'master' of https://github.com/gocardless/gocardless-python into add-currency
add currency parameter to Client.create_bill
add currency parameter to resources too
Merge pull request #21 from pegler/add-currency

Update add-currency branch