docs: fix links to stanza doc

docs/api/xmlstream/stanzabase.rst

@@ -99,8 +99,8 @@ of an interface defined by the parent.
 .. seealso::
 
     - :ref:`create-stanza-plugins`
-    - :ref:`create-extension-plugins`
+    - :ref:`is_extension`
-    - :ref:`override-parent-interfaces`
+    - :ref:`overrides`
 
 
 Registering Stanza Plugins

docs/howto/stanzas.rst

@@ -327,6 +327,9 @@ Which will produces the following:
 We can see that ``bool_interfaces`` allows to quickly create sub-elements with no
 content, without the need to create a custom class or getter/setter.
 
+
+.. _overrides:
+
 overrides
 ~~~~~~~~~
 
@@ -350,6 +353,8 @@ parent ``interfaces`` with the same name.
     parent = Parent()
     parent['toto'] = 'test' # equivalent to parent['sub']['toto'] = "test"
 
+.. _is_extension:
+
 is_extension
 ~~~~~~~~~~~~