* Added dygraph quantization.

* Added save_quant_model function

* Overload quant_aware, make dynamic and static model use the same interface.

* Use singledispatch to overload the quant aware for dygraph quantization

* Add unnitest for dygraph quant_aware

* Use 2.0 api for supporting paddle 2.0

* Using pre-commit to modify the coding style.

* Add unittest for user inputted quant_config.

* Add singledispath into requirements.txt
Co-authored-by: NBai Yifan <me@ethanbai.com>

* migrate quant code to paddle2.0

* fix quant unittest

* fix demo

* post_quant_static: remove the cache params, add optimize_model params, test=develop
Co-authored-by: NBai Yifan <me@ethanbai.com>

* fix pruned model save and load, fix bugs of pruning depthwise conv

* add unit test of pruned model save and load

* temp delete

* add unit test

* paddleslim/quant/quanter.py

* fix bug

* add out scale for quantization

* update quant_aware unittest

* update quant_aware unittest

* add quant_post_only_weight

* update quant_post_weight

* change paddle version requirments

* add test for quant_post_only_weight

* add default config and support more ops

* remove debug code

* remove debug code

* fix details

* refine quanter

* add details in doc

* check type of for_tensorrt and is_full_quantize

* add description for tensorrt