def add_files(klass)
      ext = asset_ext klass
      find_files(ext).map do |path|
        klass.new(self, path)
      end
    end
def add_files(klass)
      ext = asset_ext klass
      find_files(ext).map do |path|
        klass.new(self, path)
      end
    end
Find files based on class type and
 return an array of Classes for each file