Makes the package follow Python conventions better.

I refactored the `__init__.py` to have a `__version__` variable (and a few others) to follow [PEP 396](http://www.python.org/dev/peps/pep-0396/).

My other changes also (especially in `setup.py`) follow [PEP 8](http://www.python.org/dev/peps/pep-0008/). There's a few violations elsewhere, but mostly line length.

I also added a root doc string to the same file so when you first import it, say in IPython you can do:

```python
In [1]: import stopspam

In [2]: stopspam?
Type:       module
String Form:<module 'stopspam' from 'stopspam/__init__.pyc'>
File:       /Users/nickcharlton/Desktop/stopspam/stopspam/__init__.py
Docstring:
stopspam

A library to check IP addresses, usernames and email addresses for their
potential as spam against the http://stopforumspam.com/ database.

Copyright: (c) 2013 by Paul Hallet
License: GPL v3
```

Hopefully, I didn't break `setup.py`. I've not done enough with it to test it.