Add initial/basic docs for batches

that still needs a lot yet i'm sure, but is a start

docs/data/batch/custom.rst

@@ -3,4 +3,73 @@
 Adding a Custom Batch
 =====================
 
-TODO
+If none of the native batch types fit your needs, you can always add a new one.
+See :doc:`native` for the list of what's available.
+
+Adding a new batch type involves 3 steps:
+
+* add the batch table schema
+* add the batch handler
+* add web views for user interaction
+
+For sake of example here, we'll define a "Please Come Back" batch.  The purpose
+of this batch is to identify members who've not shopped in the store within the
+last 6 months, and generate custom coupons for each, to encourage them to come
+back.
+
+Adding the batch table schema is not much different than adding any other table
+to the DB; see also :doc:`/data/db/extend`.  Note that you should always prefix
+table names with something unique to your app, and generally speaking the word
+"batch" should go in there somewhere too.  For instance we might call them:
+
+* ``poser_batch_plzcomeback``
+* ``poser_batch_plzcomeback_row``
+
+To add the batch tables, create a new Python module.  This would go in
+``~/src/poser/poser/db/model/batch/plzcomeback.py`` for instance.  Within that
+module you then define the batch table classes.  Be sure to also define the
+``batch_key`` for the main table, which should also get the app-specific
+prefix, e.g.::
+
+   from rattail.db.model import Base, BatchMixin, BatchRowMixin
+
+   class PleaseComeBack(BatchMixin, Base):
+       __tablename__ = 'poser_batch_plzcomeback'
+       __batchrow_class__ = 'PleaseComeBackRow'
+       batch_key = 'poser_plzcomeback'
+       model_title = "Please Come Back Batch"
+       model_title_plural = "Please Come Back Batches"
+
+   class PleaseComeBackRow(BatchRowMixin, Base):
+       __tablename__ = 'poser_batch_plzcomeback_row'
+       __batch_class__ = PleaseComeBack
+       model_title = "Please Come Back Batch Row"
+
+To add the batch handler, create a new Python module.  This would go in
+``~/src/poser/poser/batch/plzcomeback.py`` for instance.  Within that module
+you then define the batch handler class.  Be sure to tie this back to the main
+batch table, e.g.::
+
+   from rattail.batch import BatchHandler
+   from poser.db import model
+
+   class PleaseComeBackHandler(BatchHandler):
+       batch_model_class = model.PleaseComeBack
+
+To add the web views, also create a new Python module.  This one would go in
+``~/src/poser/poser/web/views/batch/plzcomeback.py`` for instance.  Within that
+module you then define the batch master view class.  Be sure to tie this back
+to both the batch and row tables, as well as the handler, e.g.::
+
+   from tailbone.views.batch import BatchMasterView
+   from poser.db import model
+
+   class PleaseComeBackView(BatchMasterView):
+       model_class = model.PleaseComeBack
+       model_row_class = model.PleaseComeBackRow
+       default_handler_spec = 'poser.batch.plzcomeback:PleaseComeBackHandler'
+       route_prefix = 'batch.poser_plzcomeback'
+       url_prefix = '/batches/please-come-back'
+
+   def includeme(config):
+       PleaseComeBackView.defaults(config)