nodejs stream 背压处理学习

内容是nodejs 官方的，对于需要开发自己的stream 是很值得学习参考的

参考资料

https://nodejs.org/en/docs/guides/backpressuring-in-streams/
https://nodejs.org/docs/latest/api/stream.html#stream_readable_pipe_destination_options
https://nodejs.org/api/stream.html#stream_buffering
https://nodejs.org/docs/latest/api/stream.html#stream_implementing_a_readable_stream
https://nodejs.org/docs/latest/api/stream.html#stream_implementing_a_writable_stream