add release notes

sphinx/source/docs/releases/0.12.5.rst

@@ -59,28 +59,39 @@ removed, as well as the following properties of ``Plot``
 * ``title_text_font``
 * ``title_text_font_size``
 
-``abstract`` moved
-~~~~~~~~~~~~~~~~~~
+Document and Model Refactoring
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In order that ``document.py`` and ``models.py`` only contain things that might
+be of usual interest to users, some changes and rearrangements were made.
 
 The ``abstract`` class decorator was moved from ``models.py`` to
-``has_props.py`` in order that ``models.py`` only contain classes that might
-be of normal interest to users. The class decorator now also adds an
-admonition to the docstring of any class marked abstract that it is not
-useful to instantiate directly.
+``has_props.py``. The class decorator now also adds an admonition to the
+docstring of any class marked abstract that it is not useful to instantiate
+directly.
+
+The metaclass ``Viewable`` has been renamed to ``MetaModel``.
 
-JQuery removed from BokehJS
-~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The ``document.py`` module has been split up, and parts that would not be of
+normal interest to most users have been moved to better locations.
 
-JQuery has been removed as a build dependency of BokehJS, resulting in a ~10%
-reduction in the size of the minified code. The variable `Bokeh.$` is no
-longer available. If you require JQuery (i.e. for a custom extension or when
-using the JavaScript API) you will need to provide it explicitly.
+These changes are not expected to impact user code in any way. For complete
+details see :bokeh-pull:`5786`.
 
-underscore.js removed from BokehJS
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+JQuery and underscore.js removed from BokehJS
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+JQuery has been removed as a build dependency of BokehJS. The variable
+`Bokeh.$` is no longer available. If you require JQuery (i.e. for a custom
+extension or when using the JavaScript API) you will need to provide it
+explicitly.
 
 underscore.js has been removed as a build dependency of BokehJS. The variable
-`Bokeh._` is no longer available. If you require underscore.js (i.e. for a custom
-extension or when using the JavaScript API) you will need to provide it explicitly.
+`Bokeh._` is no longer available. If you require underscore.js (i.e. for a
+custom extension or when using the JavaScript API) you will need to provide it
+explicitly.
+
+Both of these removals together result in a ~10% reduction in the size of
+the minified BokehJS library.
 
 .. _project roadmap: http://bokehplots.com/pages/roadmap.html