Configure legend box for too many legends

[v0dro]

If there are too many legends, for example in this spec:

      it "adjust legends if there are too many", focus: true do
        @figure = Rubyplot::Figure.new
        axes = @figure.add_subplot 0,0
        axes.title = "My graph."
        [
          [[1, 2, 3, 4, 4, 3], 'Apples oranges Watermelon'],
          [[4, 8, 7, 9, 8, 9], "Oranges"],
          [[2, 3, 1, 5, 6, 8], "Watermelon"],
          [[9, 9, 10, 8, 7, 9], "Peaches"]
        ].each do |d, name|
          axes.bar! do |p|
            p.data d
            p.label = name
          end
        end
        axes.x_ticks = ['2003', '', '2004', '', '2005']
      end

The legend box should properly be configured such that it is displayed appropriately.

Also make sure MultiBar handles legends.