* Add CheckpointReader and corresponding C APIs.
* Add essential components of SavedModel format loading.
* Add checkpoint reading for SavedModel format loading.
* Revise customized json converters.
* Add support for loading models from python.
* Fix the duplicated weights in Keras.Model.
* Add alexnet loading test and check for loaded weights.
* Fix ci error caused by branch merge.
* Resolve the comments and errors.
* Fix the stucking of training when loading model.
* Fix the stucking of training when loading model.
* fix intptr.
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Co-authored-by: Haiping Chen <haiping008@gmail.com>