* speedup gc and inplace softmax_with_cross_entropy_grad
test=develop

* refine models gpu mem
Merge skip vars and warning messages of mem opt
remove relu mem opt
test=develop

* follow comments
test=develop

test=develop

* Split test_calibration test to two tests

test=develop

* Modify CMakeLists file
test=develop

test=develop, add CMAKE

* Support seq len equal to 0 in sequence ops

test=develop

* Add more test cases

* Fix some comments

test=develop

* Fix py3 error

test=develop

Fix dy sl bug

disable runtime_context_cache pass by default

* Check some shapes only in runtime

test=develop

* Follow review comments

test=develop

* Update API spec

test=develop

fix trt anakin subgraph compile rely

* fix cmakelist detecting problems

* test=develop

* test=develop

test=develop

fix bug of num > INT_MAX

test=develop

Add nccl context pybind

Fix dygraph checkpoint bug

use multi-thread to speedup CI tests

Fix test_profiler when the machine has many cores.

Refine ENFORCE in infer_shape of gru_op and lstm_unit_op.

fix logical op infershape

disable test_elementwise_mul_mkldnn_op case

imperative fix tracer train mode

test=develop

* fix sampling id op bug, test=develop

Improve preprocessing script and read from tar

* fix overflow by int32 mul test=develop

* fix reference nullptr

* fix codestyle test=develop

* modify to point in ContextProjectFunctor test=develop

* modify to point in ContextProjectFunctor test=develop

* modify . to -> test=develop

fix infershape bug

test=develop

Fix infer shape of split lod tensor op

fix teacher_student op infer

Fix bpr loss