[IMPROVEMENT] Raises targetSdkVersion to API 27
[IMPROVEMENT] Adds error code for duplicate foreign transaction id - SumUpAPI.Response.ResultCode.ERROR_DUPLICATE_FOREIGN_TX_ID
[IMPROVEMENT] Adds error code for invalid affiliate key - SumUpAPI.Response.ResultCode.ERROR_INVALID_AFFILIATE_KEY
[API CHANGE] SumUpPayment.productAmount(double) is deprecated in favor of SumUpPayment.total(BigDecimal)
[API CHANGE] SumUpPayment.productTitle(String) is deprecated in favor of SumUpPayment.title(BigDecimal)
[API CHANGE] SumUpApi.openPaymentActivity(Activity activity, SumUpPayment payment, int requestCode) is deprecated in favor of SumUpApi.checkout(Activity activity, SumUpPayment payment, int requestCode)
[FIXED] A compilation problem highlighted in issue #6 - Workaround described there is no longer necessary