enhance DataFeeder

Polish the doc of cross_entropy

* Rename API of DeviceContext

Make them as usual names.

* Rename API of DeviceContext

Make them as usual names.

* Fix compile

* Fix compile

* Fix compile

* Fix compile

* Fix compile

* "fix data transform"

* "split into next PR"

Add conv2d_python doc

* fix bugs

refine CMakeLists.txt when add op need DEPS

Fix two docs

* add KernelTypeToString interface

* cache memory in local scope

* fix typo

* refine trans logic

[WIP] new backward

Optimize the rowwise add function.

fix dist train trainspiler bugs

* "refine kernel registrar"

* "refine registrar with multikey"

* "fix register"

* "refine multikernel register"

* "fix CI"

* "fix CI"

* "fix registry"

* "swtich GPU to CUDA"

* "add register macro test case"

* "fix CI"

Refine drop_out_op and batch_norm

* add memory switch mechanism in operator kernel switch

Rename output of softmax and activations

Add data type checking for io.save_inference_model()

* init data_transform

* complete DataTransform

* fix build error

* add data_transform_test

* add a register test for data_transform_fn

* use function to simulate registration macro

* add register macro

* update test

* clean code

* restore unrelated code

* update data transform test

* generate unique name for REGISTER_DATA_TRANSFORM_FN

* add const

* follow comment

* update KernelTypePair hash function