PEP-8 conformance improvements

This pull request puts a dent in the task of making scipy pep8 compliant.

The latest version of pep8.py (https://github.com/jcrocholl/pep8) uses the tox.ini configuration file, so I've added a [pep8] section. This section lists 

 - SWIG generated .py files which we want to ignore. 
 - Error codes which are currently failing which should be ignored. As such, running "pep8 scipy" returns no errors (a good thing!)

Over time we should aim to have "pep8 scipy" passing with fewer ignore error codes.