* add mul and matmul quantization, test=develop
* add test for matmul, test=develop

* fix post training quantization bug of memory constrained, support the input be different, test=develop

* support set model_filename and params_filename in post_training_quantization, test=develop

* Support  more ops in post training quantization, and save the output scale in quantized op.
* Update docs in post training quantization and qat 

* add post training quantization, test=develop
* specify the quantizable op type, test=develop