Add some more "handler" docs

app handler, batch handlers, native batch types, people handler

docs/data/batch/native/newproduct.rst

@@ -0,0 +1,16 @@
+
+New Product Batch
+=================
+
+**Batch Type Key:** ``newproduct``
+
+**Purpose:** Import new products into the system.
+
+**Default Handler:** :class:`~rattail:rattail.batch.newproduct.NewProductBatchHandler`
+
+Data for this batch usually comes from a spreadsheet file.  It should
+contain new product records, with all necessary data for each.
+
+Executing this batch may just create the item in Rattail by default.
+You may want to use a custom handler for inserting the item directly
+to your POS system instead, for instance.