twMove( Vert, Horz )
 ----------------------------------------------------------------------------
     Moves a window a specified number of vertical and horizontal
     spaces. Bounds checking is carried out to make sure the image
     remains in video RAM. This function may be used in a UDF to create
     a user controlled window moving function by defining a SET KEY.
     Positive and negative numbers define right/down and up/left
     respectively.

     IF THE WINDOW CARRIES SHADOW INFORMATION, IT IS UPDATED AS THE
     WINDOW MOVES.

       Arguments:

     Vert - 'N' Number of places to move vertically.  Defaults to 0.

     Horz - 'N' Number of places to move horizontally.  Defaults to 0.

     One of these must be passed for the function to perform anything.

       Return:

     Current window handle

       Example:

     twMove( 10, 0 )

        Moves the current window ten spaces down.

     twMove( -2, 30 )

        Moves the current window up two lines and right thirty.