Called by the framework from within the Run member function to exit this instance of the application.
The application's exit code; 0 indicates no errors, and values greater than 0 indicate an error. This value is used as the return value from WinMain.
Do not call this member function from anywhere but within the Run member function.
The default implementation of this function writes framework options to the application's .INI file. Override this function to clean up when your application terminates.