…he Xero API.
…ms. Now a helper method XeroGateway::Invoice#add_line_item(params).
…nvoice. Should be able to work with invoice.contact without helper methods and without the Contact instance being initialized when the Invoice instance is initialized.
…ingle API request.
…ontacts with a single API request.
…tacts that may have changed since the passed in date/time (although only the date part appears relevant at the moment.
* Updated Invoice class to calculate sub_total, total_tax and total automatically. * Added unit test cases for the above changes. * Updated README and gateway.rb comments to reflect these changes to the API. * NOTE: This should be backwards compatible with current implementations using this library as the setters for these values still exist (even though they don't do anything) and these values need to be accurate for the Xero API calls to succeed anyway.