Show Savon HTTP request logs when :test_mode = true
Allow multiple customs lines to be added to a military/international indicium. 

Stamp.create!(
  ...
  :rate => {
    :customs => {
      content_type: 'Merchandise',
      :customs_lines => {
        :custom => [
          { :description => 'Item A', :quantity => 1, :weight_oz => '1', :value => 2.00 },
          { :description => 'Item B', :quantity => 1, :weight_oz => '2', :value => 1.00 }
        ]
      }
    }
  }
  
)