added weight-exchange library

dnn/torch/weight-exchange/README.md

dnn/torch/weight-exchange/requirements.txt

dnn/torch/weight-exchange/setup.py

dnn/torch/weight-exchange/wexchange/__init__.py

dnn/torch/weight-exchange/wexchange/c_export/__init__.py

dnn/torch/weight-exchange/wexchange/c_export/c_writer.py

dnn/torch/weight-exchange/wexchange/c_export/common.py

dnn/torch/weight-exchange/wexchange/tf/__init__.py

dnn/torch/weight-exchange/wexchange/tf/tf.py

dnn/torch/weight-exchange/wexchange/torch/__init__.py

dnn/torch/weight-exchange/wexchange/torch/torch.py