Added in instructions on how to get python reqs and a requirements.txt file

Makes it easier to use a new virtualenv

fix argparse/imports for python3 in demo.py

Imported pdb twice, removed one

removes cPickle import (unused in demo and would require different
import for Python3) and updates argparse calls to remove REMAINDERS
(allows user to manually specify load_dir/image_dir)

In __init__() save self.num_data for use in __len__()

datasets.vg() —> vg()

The class __vg()__ is defined in this file.

Typo: pickl --> pickle

Modernize Python 2 code to get ready for Python 3