* imporve error messages for conv, conv_transpose, cos_sim, group_norm

reduce the pricision of test case for matmul

The flaky windows test is hard to debug. It just has an exit code 0xc0000374 without any log so we don't know where and why. The probability of failure is about 1/50.

I spent 3 days and found it happened only when using PE + control flow + Windows. Exit code 0xc0000374 indicates heap corruption or access violation, but I found the memory is enough during debugging. There is no failed test under 500+ linux tests. I suspect the reason is multiple thread difference between Windows and Linux but I don't have time to completely debug it now. I will temporary disable the test and fix it in next days.

* err msg enhance for PRelu

* add ut
test=develop

* err msg enhance for GRUUnit

* add ut
test=develop

* err msg enhance for Embedding

* add ut
test=develop

* err msg enhance for BilinearTensorProduct
test=develop

* rebase dev
test=develop

* add ut
test=develop

* fix program sample code error, test=develop, test=document_fix

* fix detail error, test=develop, test=document_fix

* fix typo, test=develop, test=document_fix

* fix compiled program sample code error, test=develop, test=document_fix

* remove cn code in doc, test=develop, test=document_fix

* API/OP (append_backward) error message enhancement test=develop

* polish check_type test=develop

* fix unittest failed test=develop

* merge develop test=develop

* Refine mechanism of calling outer function test=develop

* fix typo test=develop

* add dist op

add addmm op

C++ OP enhancement.

* add tdm sampler op

* fix compile bug

* fix compile bug

* fix compile bug

* fix compile bug

* test=develop, add tdm sampler unittest

* fix tdm sampler unittest

* fix input var name bug

* update tdm sampler unittest

* fix unittest

* fix unittest

* update tdm sampler unittest

* add tdm exe run unittest

* fix infershape

* test=develop, add doc

* test=develop, fix gcc8 compile bug & unittest bug

* test=develop, fix unittest

* test=develop, fix T one & zero

* test=develop, add unittest check

* test=develop, add doc smaple code & fix dype set

* test=develop, fix dtype

* test=develop, fix compile bug

* test=develop, fix unittest

* test=develop, fix unittest

* test=develop, check py3 unittest

* test=develop,fix unittest

* test=develop, fix py3&py2 unittest diff

* test=develop, fix sample code

* test=develop, fix sample code

* test=develop, fix sample code

* test=develop, fix error message

test=develop

* refine example code in en doc, test=develop, test=document_fix

* update shape to make it meaningful, test=develop, test=document_fix

* add instance_norm op for dygraph, test=develop

* add error message, test=develop

* add LayerList insert and extend
test=develop

* add index range check
test=develop

* add sample codes
test=develop

* refine sample code
test=develop

* fix init_gflags with 'python -c', test=develop

* enhance error msg related Tracer, test=develop

* refine err msg, test=develop

* follow comments, test=develop

* API(to_variable/save_dygraph) error message enhancement

error message enhancement for fusion_seqpool_concat_op

error message enhancement for py_func op. 

* Involves AfsAPI to resolve slow downloading.
* Mainly used in PaddleBox