def each(&block)
      files.each(&block)

      directories.each do |subdirectory|
        block.call(subdirectory)

        subdirectory.each(&block)
      end
    end
def each(&block)
      files.each(&block)

      directories.each do |subdirectory|
        block.call(subdirectory)

        subdirectory.each(&block)
      end
    end
Iterates through this +Directory+'s children depth-first

 @yieldparam child [File, Directory]