That api has been removed (it was really only useful for a small set of games). If you want to create gridlines try this:

def gridlines!
  args = $gtk.args
  args.state.show_gridlines = !$gtk.args.state.show_gridlines
  if args.state.show_gridlines && args.outputs.static_lines.length == 0
    args.outputs.static_lines << 80.times.map do |i|
      [
        [i * 16,      0, i * 16,    720, 128, 128, 128],
        [     0, i * 16,   1280, i * 16, 128, 128, 128],
      ]
    end
  elsif !args.state.show_gridlines
    args.outputs.static_lines.clear
  end
end

Then you can bring up the heads up display and run grindlines! and press enter.

Also! Come to the Discord channel if you have questions (lots of people there to help): http://discord.dragonruby.org.