def package(id, &block)
      unless block
        raise InvalidValue.new(:package, "have a block")
      end

      packagers[id] << block
    end
def package(id, &block)
      unless block
        raise InvalidValue.new(:package, "have a block")
      end

      packagers[id] << block
    end
Add or override a customization for the packager with the given +id+. When
 given multiple blocks with the same +id+, they are evaluated _in order_,
 so the last block evaluated will take precedence over the previous ones.

 @example
   package :id do
     key 'value'
   end

 @param [Symbol] id
   the id of the packager to customize