Sync this repo with book's code lists & snips

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Hi, I and my friends nearly finish the translation, and we are syncing the code samples in the book and put them online.

A preview is here: http://rdp.reactiveplatform.xyz/chapter-03/index.html

But there is a problem that, some code lists and snips are not lives in this repo, So I have to manually recreate them, like, https://github.com/ReactivePlatform/reactive-design-patterns-cn/blob/master/chapter03/src/main/java/chapter03/UsingStringBuffer.java

Hopefully, we could rely on some of your great works and then make PR to merge back:) I did that before for Netty In Action book, eg: https://github.com/normanmaurer/netty-in-action

Thank you, your input is very needed.

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downstream work here :https://github.com/ReactivePlatform/reactive-design-patterns-cn