add --binary option and ability to open .gz and .bz2 input files

Hi Bryan,

Thanks for DeepWalk. I was pleased to see a real useable implementation released with the paper.

I wanted to test DeepWalk a bit but I typically gzip my data files so I added support for that and also the ability to save the resulting model to word2vec's (more compact) binary format.
There is also a bit of whitespace cleanup in graph.py

Let me know if you see any issues here.
Travis