* add python example for face detection part

为了方便二次开发，这里添加了直接使用Python脚本的形式进行人脸检测的示例。

* change the demo image

* fix link

* slove_readme_link_useless

* support no label training

* fix load_crowd

* update to fit rbox

* add empty_ratio

* update configs

* support mask rcnn

* clean drop_empty for mot & keypoint

* refine is_crowd

* unify log_smooth_windows and log_iter

test=develop

* remove duplicate log_iter

* remain mobile yml, since they are soft-link

test=develop

* add blazeface_nas1

* fix all documentation

* fix docs conf.py

* fix some error

* fix readthedocs

* add blazeface nas demo

* fix format

* fix configs

* fix reduce_rate

- 1.add cn docs
- 2.fix fddb evaluate
- 3.fix get_shrink
- 4.delete FLAGS.dataset_dir

* add step in prior_box

* refine README

* Polish Reader to simplify preprocessing logic.
#  sample_transforms-> make batch -> batch_transforms in Reader.
* Clean some code
* Imporve yolov3_r50vd_dcn_obj365_pretrained_coco 41.4 to 41.8.
* Update all configs.

* update face_eval_data

* update code & doc

* add face doc
* update face detection readme and add demo jpg

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