code: def parse_generator_doubling(config):
      
      start = 1
      if 'start' in config:
          start = int(config['start'])
  
      # We cannot simply use start as the variable, because of scoping
      # limitations
      def generator():
          val = start
          while(True):
              yield val
              val = val * 2
      return generator()
docs: Returns generators that double with each value returned
          Config includes optional start value