How to create custom shapes with custom connection points for DiagramDesignerControl

The Diagram control supports a special language for defining shapes. The main element that contains shape description is ShapeTemplate. This element describes a shape contour and may contain several segments:
- Start. Specifies the start point
- Line. Defines a line with start and end points
- Arc. Defines an arc with start and end points

To specify connection points, use the ShapeTemplate.ConnectionPoints property.
To register custom shapes, create a stencil with the DiagramStencil.Create method and pass it to the DiagramToolboxRegistrator.RegisterStencil method.