* fix recurrent bug
test=develop

* add expand_as op, test=develop

* add expand_as op,test=develop

* add expand_as op,test=develop

* add nn.py, test=develop

* delele paddle_enforce, test=develop

* refine py_reader exit, test=develop

* fix multiprocess_reader exception unittest, test=develop

* increase code coverage for legacy fluid.layers.py_reader, test=develop

* Refine error message of transpose.
* Fix transpose, multiplex, unsqueeze, unstack. test=develop, test=document_preview, test=document_fix

2. fix bug in backward.py: using fill_constant instead of fill_constant_batch_size_like
3. fix bug in ExpandGradOp.

test=develop

* modified group_norm's unittest for pass statement, test=develop

* fix group_norm's bug: scale or bias is None which causes segmentation fault, test=develop

* Refine create_array api en doc

test=develop
test=document_fix


* Fix api doc example bug and polish square

test=develop
test=document_fix


* Refine comment

test=develop
test=document_fix


* refine API.spec

test=develop
test=document_fix

* fix_conv_grad_grad

* fix_bug, test=develop

* support reshape doubel grad, test=develop

* fix reshape double grad, pass converage, test=develop

* fix review, test=develop

* refine eng doc for hard_sigmoid op
test=develop
test=document_fix

* refine the description of hard_sigmoid
 test=develop
test=document_fix

* update API.spec
test=document_fix

* Refine the decription of parameters of HardSigmoid op
test=develop, test=document_fix

* Update API.spec for hard_sigmoid op
test=develop, test=document_fix

* enhance embedding error message test=develop

* enforce .h error test=develop

* fix unittest code test=develop

* Fix fp16 dtype in embedding test=develop

* add import warnings test=develop

* add input type and dtype check, enhance shape error message for concat_op
test=develop

* enhance shape check
test=develop

* improve coverage

test=develop

* fix APIs: relu, relu6, hash

test=develop
test=document_fix

* fix relu6 doc

test=develop
test=document_fix

* fix API.spec

test=develop
test=document_fix

* add description link for hash

test=develop
test=document_fix

* add input type and dtype check for accuracy_op

* add input type and dtype check for accuracy_op

* modify python error on accuracy_op,add test=develop

* modify details on accuracy_op, test=develop

* test float16, test=develop

* add warning, test=develop

* enhance mul_op input error message test=develop

* fix API:cos, exp, ceil, elu, brelu English doc
test=develop
test=document_fix

* fix the precise roi poop op test=develop
add roi backward implementation, fix the output-channel

* modify english api test=develop test=document_fix

- leaky_relu
- less_than
- log
- logical_and
- logical_or
- logical_xor
- logical_not

* fix English Doc of API:layers.py_func/sum

* doc fix, test=develop, test=document_fix

fix reorder_lod_tensor_by_rank doc en 

* Fix several api docs

test=develop, test=document_fix

* fix expand bug test=develop

* fix style test=develop

* fix style test=develop

* fix style test=develop

* fix style test=develop

* modify document of 11 APIs
test=develop
test=document_fix

* fix dtype to data type and description of name parameter

* refine en doc. test=develop. test=document_fix

enhance shape error messages for reshape op.
test=develop

* remove fc_grad, test=develop

* remove fsp op since no unittests, test=develop

* add api check in fc test=develop

* enforce shape error info of sum op test=develop

* fix spelling test=develop

* print x_dims info test=develop

* enhance shape error info test=develop

* Add detailed error messages for nce layer

test=develop

* Fix some problems

test=develop

* Fix unit test coverage

test=develop

* test=develop,test=document_preview, test=document_fix

* test=develop,test=document_preview, test=document_fix

* fix API.spec, test=develop,test=document_preview, test=document_fix

* Add input check and refine error message

* Refine test case and comments

test=develop
Signed-off-by: Nzhaoyuchen <zhaoyuchen01@baidu.com>