code: public static <T> Connectable<T> schedule(final Stream<T> stream, final String cron, final ScheduledExecutorService ex) {
          return new NonPausableConnectable<>(
                                            stream).schedule(cron, ex);
      }
docs: Execute this Stream on a schedule
  
  <pre>
  {@code
  //run at 8PM every night
  Streams.schedule(Stream.generate(()->"next job:"+formatDate(new Date()))
  .map(this::processJob)
  ,"0 20 * * *",Executors.newScheduledThreadPool(1)));
  }
  </pre>
  
  Connect to the Scheduled Stream
  
  <pre>
  {@code
  Connectable<Data> dataStream = Streams.schedule(Stream.generate(()->"next job:"+formatDate(new Date()))
  .map(this::processJob)
  ,"0 20 * * *",Executors.newScheduledThreadPool(1)));
  
  
  data.connect().forEach(this::logToDB);
  }
  </pre>
  
  
  @param stream the stream to schedule element processing on
  @param cron Expression that determines when each job will run
  @param ex ScheduledExecutorService
  @return Connectable Connectable of emitted from scheduled Stream