change <torch/torch.h> to <torch/extension.h> to work on windows

[ausk]

First, thank you for your work.

1. If we include <torch/torch.h> in Pytorch 1.x , then it will complain:

#warning \
    "Including torch/torch.h for C++ extensions is deprecated. Please include torch/extension.h"

And in Windows, msvc will faild because fatal error C1021: 无效的预处理器命令“warning”.

Just change <torch/torch.h> to <torch/extension.h> will fix it.

2. Also, insted install into user directory, we can build develop insted :

#python setup.py install --user
python setup.py build develop

The result is fine.