sf_menu               Very simple, non-complex menu function
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    function int sf_menu prototype
      parameters value int lr,;
                 value int lc,;
                 value int rr,;
                 value int rc

    Very simple, non-complex menu function.  After you draw a screen of
    what will become a menu, calling this function with the correct
    parameters will turn the screen into a @...PROMPT type menu.  Sf_menu()
    returns the screen element selected or zero if escape is pressed.
    Only the up and down arrow keys function with this function.  Sf_menu()
    uses the true shadow to highlight the menu options.

    Example:

    sf_cua_text_line( "Menu Option 1", 05, 15, -16, -7, 0 )
    sf_cua_text_line( "Menu Option 2", 06, 15, -16, -7, 0 )
    sf_cua_text_line( "Menu Option 3", 07, 15, -16, -7, 0 )
    sf_cua_text_line( "Menu Option 4", 08, 15, -16, -7, 0 )
    sf_cua_text_line( "Menu Option 5", 09, 15, -16, -7, 0 )
    ? sf_menu( 5, 15, 9, 27 )