* init optimizer design

* fix index

* optimize the interface

* add a link to python_api.md

* optimize the code of Optimizer

* Implemented the hardShrink activation

* Fixing the unit test

* Add numerically-stable logsigmoid activation

* Add softshrink operator

* Adjust relative tolerance for grad-check

* Address review comments

API of GAN

Feature/parameter

Polish CompileTime InferShape

* conv_shift_op: initial implementation using Eigen

Limitations:
- both gradient outputs must be specified and are always computed
- explicit for loops => could be optimized in various ways
  (e.g., different memory layout)

* conv shift - gradient fixes

fix case when not all output gradients desired

* conv shift: minor cleanup

* conv shift - more minor cleanup

* conv shift: clean up & initial GPU implementation

* fix rebase issue

Init Python API

Fix OpDesc bug

remove unused PADDLE_ONLY_CPU comments

fix InferShapeContextBase to InferShapeContext

Add max pool op (with index)

Removed unreached code

ELU activation

1. InferShape should be a method for `OpDescBind` not `Operator`, since
  `OpDescBind` is a compile-time concept.
2. Pre-create operators and store them into a map. Make InferShape
   faster