a bugfix of img_aug.py and add a img_crop.py

[zzdyyy]

1. bugfix of img_aug.py: Augmentor 0.2.8 needs absolute target path
2. add img_crop.py to automate the cropping, splitting of CUB_200_2011
3. modify the instructions for preparing the data

[Yung-zi]

I tried your method. However, an error still occurred in "img_aug.py". The error is listed as follows.

raise IndexError("There are no images in the pipeline. "
IndexError: There are no images in the pipeline. Add a directory using add_directory(), pointing it to a directory containing images.