Add hosted_invoice_url

[tiezkoz]

Thank you for creating the library!

Is it possible to add hosted_invoice_url to the invoices?
https://docs.ecurring.com/invoices/get/

It would really make my day!

[tdgroot]

@tiezkoz thank you for your suggestion!

Please, feel free to make a contribution so you can make use of this feature sooner than later!

Otherwise, we'll keep this suggestion in mind when we work on this package.