Created by: zhiqiu

PR types

Function optimization

PR changes

APIs

Describe

Refine paddle.stack API

• Variable -> Tensor
• use core.ops.stack in dygraph mode
• refine document
• fluid.layers.stack(x, axis=0) -> fluid.layers.stack(x, axis=0, name=None), which is compatible upgrade.
• reuse code of fluid.layers.stack