[Feature] add onnxruntime test tool (#498)

* add onnxruntime test tool, update pytorch2onnx to support slice export

* onnx convert with custom output shape, update test code

* update pytorch2onnx, add rescale_shape support, add document

* update doc for lint error fixing

* remove cpu flag in ort_test.py

* change class name, fix cuda error

* remote comment

* fix bug of torch2onnx

* mIOU to mIoU