ONNX ResNet example (intel-analytics#2939)

* add onnx resnet example

* add doc for onnx

* add doc for onnx

* clean up

python/bigdl/dllib/examples/onnx/README.md

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+# ONNX ResNet-50 Model Loading in BigDL
+
+
+## Download model file
+ * [Download model](https://s3.amazonaws.com/download.onnx/models/opset_9/resnet50.tar.gz)
+ * Uncompress the file
+    ```
+        tar -zxvf resnet50.tar.gz
+        
+        .
+        ├── model.onnx
+        ├── test_data_set_0
+        ├── test_data_set_1
+        └── ....
+    ```
+
+## How to run this example:
+ * Import library dependencies
+```
+import numpy as np
+from bigdl.contrib.onnx import load
+```
+
+ * Set target ONNX ResNet-50 model path
+ ```
+ restnet_path = "uncompressed/file/path/model.onnx"
+ ```
+   
+ * Load ONNX ResNet-50 model into BigDL
+ ```
+ restnet = load(restnet_path)
+ ```
+ 
+ * Create a sample tensor and pass it through loaded BigDL model
+ ```
+ restnet_tensor = np.random.random([10, 3, 224, 224])   
+ restnet_out = restnet.forward(restnet_tensor)
+ ```
+ 
+ 
+## Known issues:
+  * ONNX feature only has Python API in BigDL.
+  * Loaded ONNX model is limited for inference.
+  * Most of operators defined in ONNX are not being supported by BigDL for now.
+  * Missing feature of exporting BigDL model into ONNX format.
+  

python/bigdl/dllib/examples/onnx/__init__.py

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+#
+# Copyright 2016 The BigDL Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#

python/bigdl/dllib/examples/onnx/load_onnx_resnet.py

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+#
+# Copyright 2016 The BigDL Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+import numpy as np
+from bigdl.contrib.onnx import load
+
+
+def load_onnx_resnet():
+    restnet_path = "./resnet-50.onnx"
+    restnet_tensor = np.random.random([10, 3, 224, 224])
+    restnet = load(restnet_path)
+    restnet_out = restnet.forward(restnet_tensor)
+    return restnet_out
+
+
+if __name__ == "__main__":
+    load_onnx_resnet()