Merge pull request !2236 from 李鸿章/callback

Merge pull request !2262 from yanghaitao/yht_fasterrcn

Merge pull request !2250 from guozhijian/fix_db_close_fail

Merge pull request !2148 from wangqiuliang/fix-hook-bprop-issue

Merge pull request !2199 from Simson/push-to-opensource

Merge pull request !2179 from YuJianfeng/all_reduce_index

Merge pull request !2193 from wenkai/wk1_log_level_0617

Merge pull request !2237 from wandongdong/master

Merge pull request !2163 from Xiaoda/3-changing-embeddinglookup-internal

Merge pull request !2229 from zyli2020/add_ftrl_op

Merge pull request !2226 from zyli2020/add_adam_op

Merge pull request !2235 from zyli2020/add_sigmoid_cross_entropy_with_logits_grad

Merge pull request !2234 from zyli2020/add_sigmoid_cross_entropy_with_logits

Merge pull request !2212 from dengwentao/embedding

Merge pull request !2200 from zjun/code_review

Merge pull request !1833 from Giancarlo/pattern_matcher

Merge pull request !2219 from jiangjinsheng/vm_splitv

Merge pull request !2256 from JesseKLee/sampler

Merge pull request !2198 from h.farahat/mask_op

Merge pull request !2255 from Peilin/bucket-batch-doxygen-fix

Merge pull request !2142 from Tinazhang/reorg-visualize

Merge pull request !2247 from yanghaoran/master

Merge pull request !2249 from ms_yan/numpy_slice_repair

Merge pull request !2092 from qianlong21st/june_third

Merge pull request !2242 from panfengfeng/modify_info_level

Merge pull request !2164 from lianliguang/master

Merge pull request !2225 from VectorSL/shape-check

Merge pull request !2243 from panfengfeng/revert-merge-2189-master

Merge pull request !2227 from jjfeing/master

Merge pull request !2238 from guozhijian/fix_doc_format

Merge pull request !2192 from baihuawei/cpulstm

Merge pull request !2210 from limingqi107/max_device_memory_optimize

Merge pull request !2183 from limingqi107/gpu_pynative_optimize