* Adding thresholded_relu op
* Adding test for thresholded relu op

* init

* unify CopyFrom interface

* fix gpu build error

* fix bug in tensor_py.h

* refine code comments and add TODO list

* fix conflicts in FeedOp and FetchOp

Explose check_attr to Python

expose AppendBackward of ProgramDesc to python

Update annotations of layers.py.

Add the sequence_concat operator.

fix executor_test build failed

Add margin rank loss operator

use protobuf_lite druning inference

Fix pool op doc and class declarations

fix Compile error [fatal error: boost/range/adaptor/reversed.hpp]

Simplify backward when inserting a sum operator to accumulate all duplicated variables

Add vol2col functor

* implementing softplus

* small fix

* small fix

* small fix

* small fix

Executor interface design and implementation

* Design doc of SelectedRows

* Follow comments

* Update protobuf message

* Follow comments, seperate LoDTensorDesc and SelectedRows Desc