Added Py2/Py3

Addressing #153.
Version only added for packages/libraries which state their version on their PyPI page. 
For instance, the PyPI page for [virtualenv](https://pypi.python.org/pypi/virtualenv) has this text:
```
Programming Language :: Python :: 2
Programming Language :: Python :: 2.6
Programming Language :: Python :: 2.7
Programming Language :: Python :: 3
Programming Language :: Python :: 3.1
Programming Language :: Python :: 3.2
```
Only added versions to libraries/packages that list support for both 2 & 3.