Get returns the details of an invoice.

GetNext returns the upcoming invoice's properties.

List returns a list of invoices.

ListLines returns a list of line items.

New POSTs new invoices.

Pay pays an invoice.

Update updates an invoice's properties.

Client is the client used to invoke /invoices APIs.

Iter is an iterator for lists of Invoices.

LineIter is an iterator for lists of InvoiceLines.