* update api format
test=develop

* update API.spec
test=develop

fix data feed ptr runtime error, pipeline trainer will core in some cases, so set it nullptr as default value.

test=develop

1. some key generation method is not aligned with PR#17965
2. enlarge ptr lifetime to avoid memory release if SetBlob fails
   otherwise it will get core dump.

test=develop

* add_elementwise_add_inplace_test,test=develop

* rename file, test=develop

* test=develop, add some comments for Program.clone

* test=develop, add API.spec

* test=develop, refine comments

* refine Program doc and clone doc

* test=develop, refine doc

*  add cuda_is_available
test=develop

* Fix api.spec
test=develop

* fix api doc
test=develop

Fix dygraph show style for FluidDoc.

* add dependecy of collective_helper

* test=develop
fix dependecy of collective_helper

* update pe reduce config
test=develop

*  drop the local_exe_scopes of the previous parallel_executor
test=develop

* add is_runnning in communicator, test=develop

test=develop

* fix prepare context redundant code problem, optimize executor by caching create_varaiables
test=develop

* supports collective training in executor

* make fetch_list runable with variables, add more unittest for use_program_cache
test=develop

* fix comment
test=develop

* use unique name for nccl_id

* supports output to stream in program_to_code

* insert sync_comm_stream before regularization; add skip_op_callstack capability in program_to_code

* set op role in collective training

* add collective op role

* remove orig file

* add build optimizer by strategy

* add collective strategy

* refine collective strategy

* add multi-process role maker

* refine strategy building factory so that we can easily plugin more strategy

* scale loss grad in collective sgd transpiler

* add support for distributed fc

* code format

* revert some features for dist fc

* add support for distributed fc training

* fix prepare context redundant code problem, optimize executor by caching create_varaiables
test=develop

* supports collective training in executor

* make fetch_list runable with variables, add more unittest for use_program_cache
test=develop

* use unique name for nccl_id

* supports output to stream in program_to_code

* insert sync_comm_stream before regularization; add skip_op_callstack capability in program_to_code

* set op role in collective training

* add collective op role

* fix comment
test=develop

* remove orig file

* add build optimizer by strategy

* add collective strategy

* refine collective strategy

* add multi-process role maker

* refine strategy building factory so that we can easily plugin more strategy

* scale loss grad in collective sgd transpiler

* add support for distributed fc

* code format

* revert some features for dist fc

* add support for distributed fc training

* test=develop
add collective op unittest standard

* test=develop
remove the test_collective directory

* test=develop
remove the test_collective directory

* remove slicegather test

* code format for reducescatter

* update attr of shard_index_op

* Modify macro nccl_helper

* remove test without distribute

* macro collective_helper

* marcro update

* test=develop
update support python3.5

* test=develop change gpu memory use to 0.1 when test

* test=develop
update ut equal func

* test=develop
set flags to 1.5

* test=develop fix pickle dumple  py35

* test=develop
fix divide in slice and add sync_comm_stream
update atol and rtol to 1e-05
rm shard_index op and test
modify read input from file to read from memory
remove origin_program in framework and add i/o in c_sync_calc_stream

* test=develop update unittest sync operator I/O

add prior_box quantization code

add scale algo rules for prior box

test=develop

* some fixes for int8 mobilenet_ssd tester
test=develop

* change wrong data file name
test=develop

* change test images bin file from 200 images to 100 images

* change directory existence to file existence during downloading
test=develop

* reuse download_data
test=develop

* run full dataset when iterations=0
test=develop

* - Reusing of reuder used in elementwise_add_mkldnn

- Added MKL-DNN sum prim reusing

test=develop

- Compilation fixes

test=develop

- Yet another compilation fix

test=develop

- Yet another compilation fix

test=develo

- Yet another linking fix

test=develop

- Final compilation fix

test=develop

- lint fixes

test=develop

- Lint fixes

test=develop

* - Fixes after review

test=develop

* Simplify multi_box_head API in detection.py and remove assign op.

* refine cuda place error msg, test=develop

* use LOG(ERROR)+exit(-1), test=develop

test=develop

* Update lamb optimizer

test=develop, test=document_preview

* Regenerate api spec

test=develop, test=document_preview

test=develop

* fix softrelu doc

test=develop

* update API doc

test=develop

* sequnce mask support max length tensor input; test=develop

* add rnn_impl.py; test=develop

* add basic gru lstm unittest; test=develop

* fix api spec; test=develop

* fix sequence_mask op bug;
test=develop
test=document_preview

* change +-*x to elmentwise_op; test=develop

* add mkl flag; test=develop

* fix rnn impl bug; test=develop

* update api spec; test=develop

* fix doc bug; test=develop

* fix lstm bugs; test=develop

* optimize communicator merge sparse gradient test=develop

* revert multithread selected rows merge add test=develop

* follow comment test=develop

* fix default value of fluid.memory_optimize
test=develop

* fix api.spec
test=develop

test=develop

* Use TensorCopySync for sequence_unpad op

test=develop

* Fix the tensor memory alloc bug

test=develop

* clean build_strategy
test=develop

* DataBalanceOpHandle has been removed
test=develop

* debug

* update build_strategy.
test=develop

test=develop

add Dygraph api to api.spec

* improve doc of lstm, sequence_enumerate, softmax_with_cross_entropy, space_to_depth APIs, test=develop

* update API.spec, test=develop

test=develop
test=document_preview

1. fix the bug that out_put_var in SaveSelectedRows would be empty string
2. use merge_sparse_lookup_table to replace sum op for load_persistables_for_inference
3. fix the bug in _clone_var_in_block_ when the var is SELECTED_ROWS.

(1) use channel instead of vector/BlockingQueue in Dataset，to keep same with existing implementation, and make code more readable and flexible (dataset single output channel or multi output channel). one previous memory out of limit problem is cause by not release memory after training.
(2) add Record because MultiSlotType costs too much memory (80B)，fix memory out of limit problem.
(3) add Channel, Archive in paddle/fluid/framework
(4) change dataset from shared_ptr to unique_ptr in pybind
(5) move create/destroy readers from trainer to dataset
(6) move shuffle from datafeed to dataset. dataset holds memory, datafeed is only for load data and feed data to network.
(7) fix thread num bug of Dataset when filelist size < thread num
(8) support set_queue_num in InMemoryDataset

* improve the doc of DataFeeder and default_main_program

* update API.spec, test=develop

* set src_idx > 0, test=develop

* add unittest and cu, test=develop