* doc add eval&infer usage

* doc fix

1. Change layers.data to fluid.data
2. Add check_version in ocr model

cherry-pick add aistudio link in README #3568 (#3585)

* add caption model ETS for PaddleVideo

* modify dynamic rnn to static rnn, and add infer past

* modify reader and configs for evaluation and validation

* modify details of the ets net code

* modify API of data and dataloader for ets net

* replace instance_norm

* add version check

* update check version

* -1->None

* fix mistake

* refine assert info in roidb_source.py

* refine image_dir assert

* fix fluid.data and fluid.io.DataLoader

* add logger in utils/utility.py

* Add face detection configs and main code.
* Integration multi-scale evaluation.

* unify reader to dataloader

* add check_version

* change PyReader to from_generator

* fluid.layers.data->fluid.data

* fix_bug

* add_multiprocess_train_to_image_classification

* Document mixed precision training flags

* Clarify GPU is required for mixed precision training

* refine build strategy for the model optimize test=develop

* fix according develop test=develop

* add CropImageWithDataAnchorSampling
* Refine bbox sampling code
* Update comments
* fix import and variable problem

* Add backbone and architecture for FaceBoxes and Blazeface.
* Add dataloader for WIDERFace dataset.