Created by: wangxicoding

PR types

Others

PR changes

APIs

Describe

1. Add paddle.sign. Deprecated paddle.fluid.layers.sign.
2. Add paddle.tanh, alias paddle.nn.functional.tanh. Add class paddle.nn.Tanh.

Doc PR and preview https://github.com/PaddlePaddle/FluidDoc/pull/2402 English doc preview: