Merge pull request !4765 from pengyongrong/modifyMemoryLeacky

Merge pull request !4764 from zyli2020/gpu_bn_op_perf_optimize

Merge pull request !4766 from chenzupeng/master-lite

Merge pull request !4640 from lyvette/parser

Merge pull request !4689 from zhangbuxue/add_check_for_user_define_bprop_in_Pynative_mode

Merge pull request !4735 from zhouyaqiang0/master

Merge pull request !4763 from gongdaguo/add_lite_models

Merge pull request !4752 from chenzhongming/lite

Merge pull request !4770 from wandongdong/master

Merge pull request !4732 from liuxiao93/fix-SoftmaxCrossEntropyWithLogits-attr-reduction

Merge pull request !4718 from fangzehua/avg0819

Merge pull request !4774 from peixu_ren/custom_pp_ops

Merge pull request !4728 from hewei/fix_tensor_to_string

Merge pull request !4734 from byweng/add_test

Merge pull request !4773 from peixu_ren/custom_bijector

Merge pull request !4476 from JesseKLee/cache_prep_branch

Merge pull request !4632 from ZiruiWu/map_callback

implment pause in MapOp, added more to callback

add ds_callback

- Initial drop of Python DSCallback

- Pybind DSCallback

- Pybind DSCallback

added callback to mapOp

- de_pipeline DSCallback

- de_pipeline DSCallback

add test case, segfault for now

fix seg fault

- de_pipeline DSCallback

remove 1 line

update callback test case, now works

use builder class for mapOp callback

- de_pipeline DSCallback

- de_pipeline DSCallback

- de_pipeline DSCallback

better test case

minor fix

add comments and minor clean ups

get rid of nullptr in MapOp, use other flag instead

fix a bug ParseMapOp only takes 1 callback

- Added WaitedDSCalabck

refactor callback param

fix text case incorrect number

- added testing

fix cpp test case

- added testing

- revert back lenet changes

- cleanup test_callbacks.py

- cleanup test_callbacks.py

fix CI stage I

fix CI stage II

fix CI and update epoch counter

- add validation
- add more testing  test_callbacks.py

use random data op to do tests

adjust when to call EpochBegin/End

- add repeat with callback

- addressing reviewers' comments

- docstring and CI fixes

- docstring and CI fixes

- docstring and CI fixes

- rebase with upstream/master

fix cpp test case

fix review comments

addr review cmts, add test case

Merge pull request !4597 from luoyang/c-api

Merge pull request !4755 from liuzhongkai/memory_leak1

Merge pull request !4703 from tom_chen/deepfm_gpu

Merge pull request !4749 from zhaodezan/master

Merge pull request !4759 from jiangzhiwen/dataset/fix_duplicate_column_names

Merge pull request !4616 from ling/deconv

Merge pull request !4756 from wangshaocong/lite_clean

Merge pull request !4685 from ZPaC/master-supports-export-server-ckpt

Merge pull request !4753 from ghzl/fix-quant-param-null