* disable memory_optimize and inpalce strategy by default, test=develop

* fix security issue
http://newicafe.baidu.com:80/issue/PaddleSec-3/show?from=page
http://newicafe.baidu.com:80/issue/PaddleSec-8/show?from=page
http://newicafe.baidu.com:80/issue/PaddleSec-12/show?from=page
http://newicafe.baidu.com:80/issue/PaddleSec-32/show?from=page
http://newicafe.baidu.com:80/issue/PaddleSec-35/show?from=page
http://newicafe.baidu.com:80/issue/PaddleSec-37/show?from=page
http://newicafe.baidu.com:80/issue/PaddleSec-40/show?from=page
http://newicafe.baidu.com:80/issue/PaddleSec-43/show?from=page
http://newicafe.baidu.com:80/issue/PaddleSec-44/show?from=page
http://newicafe.baidu.com:80/issue/PaddleSec-45/show?from=page

test=develop

* revert piece.cc, test=develop

* adjust api.cc,test=develop

* fix some comments, include cosine_decay,l2_normalize,pixel_shuffle

* Add api.spec, test=develop

* update api.spec, test=develop

* add api.spec,test=develop

* test=develop

* test=develop

* fix conflict,test=develop

test=develop

* Add an option to enable the cache of expected kernel in train phase.
test=develop

* Change the default value of cache_expected_kernel to true.

develop=test

test=develop

test=develop

test=develop

* bug-fix, test=develop

* tweak code, test=develop

list of fixed ops:
lookup_table_op
space_to_depth_op
squared_l2_distance_op
squared_l2_norm_op
teacher_student_sigmoid_loss_op
tree_conv_op
warpctc_op

test=develop

test=develop

* test fuse all_reduce

test=develop

test=develop

* Try to enable the runtime_context_cache pass in train phase.

* Put the append of runtime_context_cache pass ahead of multi_dev passes.
test=develop

test=develop

test=develop

test=develop

test=develop

add NCCLParallelContext for parallel dygraph

test=develop

test=develop

test=develop

* add pixel_shuffle op

* add pixel_shuffle op, test=develop

* rewrite code, test=develop

* delete useless comment, test=develop

* Refine pixel_shuffle_op and unit testing

* refine code,test=develop

* refine .cu,test=develop

* fix unittest,test=develop

* Fix unit testing
test=develop

* resolve conflict, test=develop

* fix test, test=develop

* fix API, test=develop

* fix test datatype bug,test=develop

* polish comments,test=develop

* add API,test=develop

* test=develop

* Add Pixel_Shuffle OP,test=develop

* support python3,test=develop

* add include memory to travis CI bug,test=develop