Constructs a WinWrapper object and attaches it to the specified window handle
| XllPlus::Forms::WinWrapper( HWND hwnd ); | 
A valid window handle.
This constructor is all that is required to initialise the object.
Because WinWrapper is a managed class, you should use gcnew
          to construct it, rather than new, as shown below.
        
System::Windows::Forms::MessageBox::Show(
    gcnew XllPlus::Forms::WinWrapper(hwnd), 
    "Hello from .NET");
      Header: xlpclrforms.h