* Enable ParallelExecutor in SSD-MobileNet and Refine code.

* Change the pre-trained model URL.

* Follow comments.

* ready to coco_reader

* complete coco_reader.py & coco_train.py

* complete coco reader

* rename file

* use argparse instead of explicit assignment

* fix

* fix reader bug for some gray image in coco data

* ready to train coco

* fix bug in test()

* fix bug in test()

* change coco dataset to coco2017 dataset

* change dataset from coco to coco2017

* change learning rate

* fix bug in gt label (category id 2 label)

* fix bug in background label

* save model when train finished

Update optimizer