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 !4759 from jiangzhiwen/dataset/fix_duplicate_column_names

Merge pull request !4696 from jiangzhiwen/jzw/c_api_csv

Merge pull request !4710 from xiefangqi/xfq_fix_tfreader_issue

Merge pull request !4498 from heleiwang/gnn_distributed

Merge pull request !4422 from xiefangqi/xfq_c++api_randomdata

Merge pull request !4392 from xychow/use-float16-in-arm-neon

try to display image

Merge pull request !4676 from xiefangqi/xfq_fix_decode_twice

Merge pull request !4638 from yanghaitao/yht_fix_weighted_sampler

Merge pull request !4625 from xiefangqi/fix_tfrecord_issue

Merge pull request !4630 from EricZ/md_tensor_from_mem

Merge pull request !4367 from MahdiRahmaniHanzaki/cutmix

Merge pull request !3769 from Alexey_Shevlyakov/ColorOp

Merge pull request !4402 from luoyang/c-api-pyfunc

Shuffle: shuffle_size -> buffer_size

Merge pull request !4322 from EricZ/bitmap_support

Merge pull request !4383 from genglishuai/genglshOK

Merge pull request !4366 from TinaMengtingZhang/cpp-api-repeat-count

Merge pull request !3753 from jiangzhiwen/dataset/csv_fix_blank_line_header

Merge pull request !3819 from jiangzhiwen/jzw/c_api_clue

Merge pull request !4311 from anthonyaje/monitor_fix

Merge pull request !3771 from cathwong/ckw_c_api_textfile_nosampler