pep8analysis

* Imports the pep8project in contrib/
* Move Set::union and Set::intersection to standard library
* Add basic testing of pep8analysis (compilation and usage) to Nit tests

TODO:
* Test execution of pep8analysis on its own test to the Nit test suite

Passes all tests on Jenkins: http://gresil.org/jenkins/job/CI%20Alexis/30/