* revise se_resnext for imagenet classification

* Add the method to train a SE-ResNeXt model

The current code can successfully implement the result of SE-ResNeXt-50.

* Update ImageNet2012 URL

* update

* update readme

* Update readme with download URL

* add unzip

* update se_resnext.py with parallel_exe

* delete train function in se_resnext.py

* add eval.py and infer.py

* move cosine_decay from se_resnext.py to train.py