* update NCE_cn.rst, PRelu_cn.rst, to_variable_cn.rst, test=develop

* fix NCE, PRelu, to_variable, test=develop

* add comment for class Layer, test=develop

* add comment for dygraph layer, test=develop

* add comment for dygraph layer, test=develop

* add comment for name, test=develop

* update to_variable_cn.rst, test=develop

* fixed one error of api_cn

* fixed some errors of api_cn

* fixed some errors of api_cn

* fixed two errors.

* fixed two errors

* fixed one error.

* fixed one error

* fixed one error.

* fixed two errors.

* fixed one error.

* fixed two errors

* fixed two links

* synchronize api_cn with the api_en of develop.

* updated develop/api_cn

* update the api_cn of develop

* update api_cn of develop

* fixed some errors

* Delete .DS_Store

* Delete .DS_Store

* Delete .DS_Store

* Delete .DS_Store

* Delete .DS_Store

* fixed some wrong links

* fixed two links

* fixed two links and some error.

* fixed some errors.

* fixed two links