Paging Get Results

[danhowellnz]

Hi Ben,

I love you work. Such an easy starting base!

I am adding in support for filtering invoices, will do a pull request once it's tidy.

I had a glance through your code and it doesn't look like it does any paging of any sort. Is that right? because the getInvoices() to my understanding would only return the first 100 records (page 1).

It would be good to build paging right into the XeroCalloutUtility. Let me know if you had any thoughts on the matter before I start meddling.

Thanks
Dan