[CHG] move things around for wider functional concern

It looks like we're going with this for the functional
documentation/mementoes thing, so move the accounting memento out of the
way and create a first draft for a documents hierarchy

double-entry.rst

@@ -0,0 +1,5 @@
+:classes: stripe
+
+=================================
+Double-Entry Inventory Management
+=================================

index.rst

@@ -5,6 +5,7 @@ Odoo Business Mementoes
 .. rst-class:: index-tree
 
 .. toctree::
-    :maxdepth: 1
+    :titlesonly:
 
     accounting
+    inventory

inventory.rst

@@ -0,0 +1,9 @@
+=========
+Warehouse
+=========
+
+.. toctree::
+   :titlesonly:
+
+   double-entry
+   valuation

valuation.rst

@@ -0,0 +1,5 @@
+:classes: stripe
+
+====================
+Inventory Valuations
+====================