* fix infer doc and config default

* refine dataset exists

* fix None proc

* Rename object_detection to PaddleDetection
* Small fix for doc

* download 3 VOC dataset

* clean code

* fix name map

* refine log

* refine dataset exists check

* add merge_and_create_list

* remove create_list

* clean code

* refine TODO

* not generate label list

* refine comment

* remove useless import

* Support download VOC dataset.

May be problematic for unattended runs.

* Unified object detection framework based on PaddlePaddle.
* Include algo: Faster, Mask, FPN, Cascade, RetinaNet, Yolo v3, SSD.