* replace and remove complex64/128 types in custom OP and other files

* fix custom_tensor_test fail bug

* fix custom_conj_test fail bug

* fix dispatch_test_op build fail bug

* add complex template file

* add numtraits for complex template

* add complex template type register

* modify specify template of complex

* modify specify template of complex

* modify specify template of complex

* modify specify template of complex

* make TensorCheckerVisitor support complex type

* fix operator= error

* add complex template

* add complex template type

* add complex template type to pyarray transform

* add complex template type to pyarray transform

* remove complex type for dlpack register

* set dlpack supprot complex type

* set dlpack supprot complex type

* set dlpack supprot complex type

* remove explict for complex constructor

* add complex unit test file

* add complex64 and complex128 type; add +-*/@ and slice opreator for complex types

* add test cases for complex elementwise, matmul and getitem unittest

* add test cases for complex types

* add test cases for complex matmul unittest

enhance reduce op which can reduce tensor with arbitrary rank 

Error description optimize for math dir

* fix softmax_with_cross_entropy cuda kernel overflow bug, test=develop

* replace old macro & for condition, test=develop

* polish details, test=develop

* support gradient accumulation of fp16 in imperative mode, test=develop

* enhance coverage test, test=develop

* follow comments, test=develop

* sequnce mask support max length tensor input; test=develop

* add rnn_impl.py; test=develop

* add basic gru lstm unittest; test=develop

* fix api spec; test=develop

* fix sequence_mask op bug;
test=develop
test=document_preview

* change +-*x to elmentwise_op; test=develop

* add mkl flag; test=develop

* fix rnn impl bug; test=develop

* update api spec; test=develop

* fix doc bug; test=develop

* fix lstm bugs; test=develop

test=develop

The macro should be defined by compiler rather than by source.

test=develop

* remove template operator

* "fix compile"

* "fix ci"

* "fix ci"

* Support int8 type.

stride should be int64_t, not int

* fix gemm error for cuda 7.5

* fix version number

* change from hgemm to gemmEx

* fix cpplint

* test cpu float16 data transform

* add isnan etc

* small fix

* fix containsNAN test error

* add data_type transform GPU test

* add float16 GPU example

* fix error

* fix GPU test error

* initial commit

* fix error

* small fix

* add more gemm fp16 tests

* fix error

* add utility function

* remove unused place

* fix ci

* add more place_test and rename Cudnn to CUDNN

* fix ci

* "derived cudnnDevice context"

* "leave remove cudnn handle from CUDADeviceContext"

* "fix math function error"

There are mainly following fixes:

- take `DeviceContext` as the template parameter of math functors and OpKernel instead of `Place`
- remove `eigen_device` interface in base class  `DeviceContext`
- remove `GetEigenDevice` interface in `ExecutionContext` and base class `DeviceContext`
- remove unused `platform::EigenDeviceConverter`
- rename `REGISTER_OP_GPU_KERNEL` to `REGISTER_OP_CUDA_KERNEL`
- rename `USE_GPU_ONLY_OP` to `USE_CUDA_ONLY_OP`