* add devices_num on reader

* refine capacity value

* refine bufsize

* enable data unittest

* exit1 in travis failed

* fix all documentation

* fix docs conf.py

* fix some error

* fix readthedocs

* refine cocoapi import

* fix infer when anno_path is None

* split yolov3 loss

* 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 x2coco.py to fix the cityscape bug when split dataset  

Fix hang bug in parallel_map.py when multiprocessing mode used and some consumer exit abnormally (#106)

* Update GETTING_STARTED_cn.md
* Update x2coco.py

* fix mixup error when dataset has only 1 sample

* refine log

* change fluid.layers.data to fluid.data

* fix export_model doc

* Optimize data transforms for yolo training

* Simplify and add docstring

* update code & doc

* change voc_loader

* add x2coco.py

* Update DATA.md

* Update DATA_cn.md

* fix the labelme2coco.py

* fix the labelme2coco.py

* add multi-scale test

* add class aware sampling strategy
* remove redundancy code

* refine assert info in roidb_source.py

* refine image_dir assert

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