Add and document attic::pulse message, and evt for sending events to the root widget.
Container tweaks, and implement VerticalSplit container.
Update sample to take advantage of the VerticalSplit container.
Correct the docstring for VerticalSplit, old one was left over from ill-fated VerticalStack attempt.
Change [Vertical]Split to be generic, update the sample to reflect this.
Correct horizontal Split composition, and add message handling for setting/toggling vertical-ness.
Add functionality to take advantage of new vertical toggle message.