Cut a release branch for v2.

[jetfuel]

As Paddle moving forward, book should also update its tutorial examples. We certainly want to keep the old example around as references.

Therefore, we should cut a release version release/0.10.0 now to indicate that all the existing example will work with paddle 0.10.0

Once the release branch is cut, we can freely update the example in develop with the fluid contents. This allows us to focus with the latest paddle fluid example and no long need to worry about v2 example. Of course, we still have the ability to update v2 examples if necessary. If we need to update any v2 example, we can still go back to the release/0.10.0 branch to update the documentation.

[shanyi15]

您好，此issue在近一个月内暂无更新，我们将于今天内关闭。若在关闭后您仍需跟进提问，可重新开启此问题，我们将在24小时内回复您。因关闭带来的不便我们深表歉意，请您谅解~感谢您对PaddlePaddle的支持!
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