GET /invoices.json | /invoices/{invoice_id}.json
tw.invoices.get(query_string, invoice_id)
tw.invoices.create(body)
PUT /invoices/{invoice_id}.json
tw.invoices.update(invoice_id, body)
DELETE /invoices/{invoice_id}.json
tw.invoices.delete(invoice_id)
PUT /invoices/{invoice_id}/complete.json
tw.invoices.complete(invoice_id)
PUT /invoices/{invoice_id}/uncomplete.json
tw.invoices.incomplete(invoice_id)
tw.invoices.currencyCodes()
PUT /invoices/{invoice_id}/lineitems.json
tw.invoices.createExpense(invoice_id, body)
PUT /invoices/{invoice_id}/lineitems.json
tw.invoices.createExpense(invoice_id, body)