Overhaul the /ordering batch API somewhat; update docs

mostly a savepoint; the /ordering API still needs some work for sure

docs/conf.py

@@ -41,6 +41,7 @@ extensions = [
 ]
 
 intersphinx_mapping = {
+    'rattail': ('https://rattailproject.org/docs/rattail/', None),
     'webhelpers2': ('https://webhelpers2.readthedocs.io/en/latest/', None),
 }