Fix some problems in api reference

Add doc for while and piecewise_decay op

add doc of sequence_softmax and parallelDo

Refine test and scope lock

* Implement a bilinear initializer for transposed convolution.

* Update some error message.

* Update some doc about layers' API.

* Fix format.

* Fix example bug in random_data_generator.

* Fix example bug in dropout.

* Follow comments and some small fix for some examples.

skip all tests in tests_parallel_executor_crf

Fix dist ut

Polish inline math and duplicable/optional in auto generated doc

Doc update

* fix mac build error

* enhance memory optimize transpiler to let users set to some skip opt set of variables

Polish documentation

fix deadlink in contribute_to_paddle_cn.rst