def set(margins)
      margins.select do |k, v|
        next unless [:left, :right, :top, :bottom, :header, :footer].include? k
        send("#{k}=", v)
      end
    end
Set some or all margins at once.
@param [Hash] margins the margins to set (possible keys are :left, :right, :top, :bottom, :header and :footer).