* dynamic send/recv selected rows

* update by comment

* fix by comment

* dist train support lr decay

* update by comment

* revert elementwise method creator

* delete comment

In notest_dist_label_semantic_roles.py, "emb" is matched with
"embedding_1.w_0", but they are two irrevalent vars.

Fixes: https://github.com/PaddlePaddle/Paddle/issues/7701

* Updating the cluster trainign doc

* Fixed few comments of transpiler

* Adding few explanations

* "fix decode bug"

* "follow commnet"

* "fix error"

* "fix hook bug"

* fix based comment

* fix copyright

* fix based on comment

* add copyright hook

* add copyright hook

* refine copyright hook

* "test copyright hook"

* fix check style

* fix ci