Add some more "handler" docs

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

docs/base/handlers/other/people.rst

@@ -0,0 +1,19 @@
+
+People Handler
+==============
+
+This handler is responsible for business logic surrounding the
+:class:`~rattail:rattail.db.model.people.Person` model.
+
+You can obtain a reference to the configured handler via
+:meth:`~rattail:rattail.app.AppHandler.get_people_handler`.
+
+You may override the default handler with config like:
+
+.. code-block:: ini
+
+   [rattail]
+   people.handler = poser.people:PoserPeopleHandler
+
+The default handler is :class:`rattail:rattail.people.PeopleHandler` -
+see its documentation for a list of methods you can override.