this adds MissingRealmError and raises if you don't set it on the
service.
make a new exception
Merge pull request #133 from mgates/error_if_no_realm

This adds MissingRealmError
Merge pull request #132 from barelyknown/delete-purchase-orders

Enable deletion of purchase orders
Merge pull request #134 from barelyknown/query-in-batches

add query_in_batches
Added section about query_in_batches