'Set title of turtle-window
Argument:
titlestring -- a string, to appear in the titlebar of the
turtle graphics window.
This is a method of Screen-class. Not available for TurtleScreen-
objects.
Example (for a Screen instance named screen):
>>> screen.title("Welcome to the turtle-zoo!")'

def title(self, titlestring):

    if (_Screen._root is not None):
        _Screen._root.title(titlestring)
    _Screen._title = titlestring
