Update Changelog

[jasongrout]

Rather than updating the changelog in PRs (where different PRs will collide), I'm keeping a list of changelog notes here to add:

Developer-oriented

• Widgets will now need correct _model_module and _view_module Unicode traits defined.
• Custom serializers in Javascript are now synchronous, and should return a snapshot of the widget state. The default serializer makes a copy of JSONable objects. (#1270)
• Selection widgets now sync the index of the selected item, rather than the label. (#1262)
• The widget protocol was significantly overhauled. The new widget messaging protocol (version 2) is specified in the version 2 protocol documentation.
• Custom serializers in either Python or Javascript can now return a structure which contains binary buffers. If a binary buffer is in the serialized data structure, the message will be synced in binary, which is much more efficient. (#1194)

User-facing changes

• Using function annotations to specify interact controls for a function is now deprecated and will be removed in a future version of ipywidgets. (#1292)
• Widgets are now displayed in the output area in the classic notebook and are treated as any other output. This allows the widgets to work more naturally with other cell output. To delete a widget, clear the output from the cell. (#1274)
• The Select widget now is a listbox instead of a dropdown, reverting back to the pre-6.0 behavior. (#1238)
• The Select and SelectMultiple widgets now have a rows attribute for the number of rows to display, consistent with the Textarea widget. The layout.height attribute overrides this to control the height of the widget. (#1250)
• Selection widgets (Select, Dropdown, etc.) now coerce their options argument to a tuple of (label, value) pairs. This makes it clearer the order in which the options will be presented. New .value, .label, and .index traits make it easier to observe or access the selected option. (#1262)
• The layout and style traits can be set with a dictionary for convenience, which will automatically converted to a Layout or Style object. (#1253)

  IntSlider(layout={'width': '100%'}, style={'handle_color': 'lightgreen'})

• Removed the version validation check since it was causing too many false warnings about the widget javascript not being installed or the wrong version number. It is now up to the user to ensure that the ipywidgets and widgetsnbextension packages are compatible. (#1219)

[jasongrout]

The changes above were merged in #1295. Let's carry on in comments below this, if needed.

[jasongrout]

New batch of changes:

• A refactoring of the text, slider, slider range, and progress widgets in resulted in the BoundedIntText and BoundedFloatText losing their step attribute (which was previously ignored), and a number of these widgets changing their _model_name and/or _view_name attributes (#1290)
• A new Password widget, which behaves exactly like the Text widget, but hides the typed text: Password(). Adding type='password' support for Text in TextView class. #1310.
• The Checkbox description is now on the right of the checkbox and is clickable. The Checkbox widget has a new indent attribute (defaults to True) to line up nicely with controls that have descriptions. To make the checkbox align to the left, set indent to False. Checkbox, RadioButton, and spacing functionality/ux improvements #1346
• In the classic notebook, output from functions triggered by a widget view is appended to the output area that contains the widget view. This means that printed text will be appended to the output, and calling clear_output() will delete the entire output, including the widget view. Regression handling callback output #1353
• The Play widget now has an optional repeat toggle button (visible by default). new: repeat button for Play widget, can be hidden #1190
• A new SelectionRangeSlider widget for selecting ranges from ordered lists of objects. For example, this enables having a slider to select a date range. Selection range slider #1356

For developers

• The widget manager clear_state method no longer has a commlessOnly argument. All models in the widget manager will be closed and cleared when clear_state is called. Delete the clear_state commlessOnly argument #1354

[jasongrout]

#1364 includes the above comment. Let's carry on below...

[jasongrout]

New batch:

#1376 - make the label width configurable, and a real label attribute
#1410 - the .id attribute containing the model id has been renamed .model_id to avoid conflicting with Backbone.
#1495 - Selection containers (tabs, accordions) now have the convention that a .selected_index of None means no container is selected
#1257 - add a new style.button_width attribute for ToggleButtons that sets the css width of the buttons. Set this to 'initial' to have buttons that individually size to the content width.

[jasongrout]

The batch of changes above went in for #1508

[jasongrout]

I put a few more notes in #1529. Since we're nearing the 7.0 release, I'll consider this issue fixed with that PR. Further additions to the changelog can just be made inline, if needed.