support for ms coco dataset

[raingo]

a working copy of voc_pascal.py for Microsoft COCO dataset.

COCO dataset should be setup by data/coco/PythonAPI/init.py

Trained models will be shared soon.

[raingo]

@rohitgirdhar It's the results of debugging. I don't know why it should be like that. There are two variables in the mat file. One is a cell array of path strings, and the other is a cell array of matrices (bbox).

[damro]

@raingo Could you please share your trained models for COCO?

[rbgirshick]

I've been working on a COCO baseline and have posted the code to the coco branch.

My version of lib/datasets/coco.py is a bit different in that it handles crowd annotations, uses the python coco api for evaluation, and supports proposals in the format generated by Hosang et al..