def cleanup(used_cache_entries)
      used = Set.new(used_cache_entries)

      Dir[@cache_dir + "/*.dat"].each do |file|
        FileUtils.rm_rf(file) unless used.include?(file)
      end
    end
def cleanup(used_cache_entries)
      used = Set.new(used_cache_entries)

      Dir[@cache_dir + "/*.dat"].each do |file|
        FileUtils.rm_rf(file) unless used.include?(file)
      end
    end
Given listing of used cache files (those that were either read
 or written during this jsduck run) removes rest of the files
 from cache directory that were unused.