* Add readme of quantization

* Fix readme of quantization, test=document_fix

[Cherry-pick]new usage of amp training. (#564)

* add quant clas

* fix load init model

* add quant

* add quant doc

* fix export model

* new usage of amp training.

* change the usage of amp and pure fp16 training.

* modified code as reviews

* add eta info

* rm duplicate desc

Fix a spelling error in the "5.2 Cutmix" document.
`rom ppcls.data.imaug import DecodeImage` to `from ppcls.data.imaug import DecodeImage`

add faq

* Add RepVGG models

* Update model code

* Rename code

* format code

* add README of RepVGG

* add faq

* add pngs

* fix mainpage

* fix faq

* update configs of ViT and DeiT

* update readme of DeiT models

* update readme of DeiT models

* update readme of DeiT models

* update README of ViT models

* Update the discription about ViT and DeiT

* Fix the error file

* Unified data format