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* fix backward compatibility by making PayuProvider's get_refund_description argument optional
* add `renewal_triggered_by` parameter to `payment.set_renew_token`
* make PayuProvider.refund fail if get_refund_description is not provided
* make PayuProvider.refund raise PayuApiError if an unexpected response is received
* deprecate the default value of get_refund_description; set it to a callable instead
* deprecate `automatic_renewal` parameter of `payment.set_renew_token`; use `renewal_triggered_by` parameter instead
* deprecate `None` value of `renewal_triggered_by` parameter of `payment.set_renew_token`; set `"user"`/`"task"`/`"other"` instead