MultiSplitterWindow class. This class is much like the standard
wx.SplitterWindow class, except it allows more than one split, so it
can manage more than two child windows.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@34634 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
