implemented CIFAR to PIL images

[jiwonac]

1. Added .gitignore
2. cifar.sh contains bash script for downloading CIFAR 10 dataset and extracting it to ../cifar directory.
3. cifar-to-resnet.py contains code for converting the 50,000 training images to a list of PIL images.

Next steps:

1. In cifar-to-resnet.py, implement a function that converts PIL images to ResNet feature vector. Img2Vec would be useful.
2. Load ResNet feature vector to FAISS.

[jiwonac]

Tagging @RosielQ @mundrapranay for review.