Include requirements.txt and automate dependencies

[tgalery]

It would be good to include a requirements.txt file and install the required dependencies when installing this library. For instance, I'm getting this error:

ImportError                               Traceback (most recent call last)
<ipython-input-1-87709484a49f> in <module>()
----> 1 import gsscraper

/usr/local/lib/python2.7/dist-packages/gsscraper.py in <module>()
      6 import hashlib
      7 import random
----> 8 import html.entities as htmlent
      9 import optparse
     10 import requests

ImportError: No module named html.entities