Merge pull request !1042 from jinyaohui/clean_pylint

Merge pull request !1082 from hewei/support_cont_break

To handle 'break' and 'continue' statement, a loop context is pushed
to a stack before we parse the loop body, and pop it after body parsed.
When a 'break', 'continue' statement is encountered, we retrieve current
loop contex from the stack, and let the current block jump to the end
block or header block;

For 'break' statement, we added an extra 'end_block' follow the 'after_block',
because 'after_block' is called from a ContionalJump in 'header_block', it can
not be set as jump target from other place. to support 'break', we let loop
body jump to the 'end_block' at the 'break' point. and 'after_block'
maybe a good place to handle loop 'else' clause in the future.

Handle 'pass' is simple, just bypass it when doing parse.

Merge pull request !1110 from lichen/fix_gatherv2_and_dataset_bug

Merge pull request !1038 from jinyaohui/clean_context

Merge pull request !1070 from liuxiao/ops-for-VM

Merge pull request !1056 from Xiaoda/memory-estimation-in-inference-phase

Merge pull request !1093 from yihuaijie/master

Merge pull request !683 from xychow/bypass-renorm-and-specialize-hypermap-parameter

Merge pull request !1062 from liuxiao/softplus-softplusgrad

Merge pull request !1050 from vlne-v1/I1GEPN-check-bprop-error-loss-scale-wrap

Merge pull request !997 from jiangjinsheng/log1p

Merge pull request !1017 from jinyaohui/context_opt

Merge pull request !766 from gongchen/nest_loop

Merge pull request !1065 from ghzl/improve-parameter-groups

Merge pull request !1075 from cathwong/ckw_dataset_ut_cleanup3

Merge pull request !1055 from jiangjinsheng/vm_floor

Merge pull request !1060 from fary86/fix_assign_target_not_parameter

Merge pull request !1034 from SanjayChan/dropout

Merge pull request !1054 from yangzhenzhang/add-slice-shape-for-param-info

Merge pull request !1048 from panyifeng/index_to_switch_case

Merge pull request !996 from Xiaoda/supporting-virtualdataset-has-three-inputs

Merge pull request !1023 from lichen/add_gatherv2_distributed_op

Merge pull request !906 from yangyongjie/master

Merge pull request !977 from yao_yf/reshape_auto_parallel_strategy_search

Merge pull request !1031 from amongo/ValueTupleOfNestedGraph

transform valuetuple to maketuple of graphs

add testcase

Merge pull request !967 from panyifeng/switch_case_primitive