message: Proposal intuitive syntax to get entities[0]
  Using the array destructuring, our code on the docs will look more intuitive, eliminating the entities[0] portion and using proper name.
diff: @@ -47,7 +47,8 @@ var invoiceObj = xeroClient.core.invoices.newInvoice(sampleInvoice);
  invoiceObj.save()
  .then(function(invoices) {
  //Invoice has been created
  - var myInvoice = invoices.entities[0];
  + var [ myInvoice ] = invoices.entities;
  + console.log(myInvoice)
  })
  .catch(function(err) {
  //Some error occurred
  @@ -77,7 +78,8 @@ currentApp.core.invoices.getInvoice(invoiceID)
  invoice.save()
  .then(function(savedInvoice) {
  - console.log(savedInvoice.entities[0].Status); //'AUTHORISED'
  + var [ mySavedInvoice ] = savedInvoice.entities
  + console.log(mySavedInvoice.Status); //'AUTHORISED'
  });
  ```
  