I have upgraded to version 1.3 this morning and my previously compiled extension was working great from start.
However, trying to compile again the code in VS 2015 gives this error:
|Error||The tag 'BurgerButton' does not exist in XML namespace 'clr-namespace:ArcGIS.Desktop.Extensions.Controls;assembly=ArcGIS.Desktop.Extensions'. Line 76 Position 14.||GFXModule||C:\Users\htudosie\Documents\Visual Studio 2015\Projects\GFXModule\GFXModule\Dockpane1.xaml||76|
I have upgraded VS with the instructions from here:
(Method: from inside VS.)
and this is what I see as the result of the installation: