Thanks @Natim for the pull-request!

About the doctests, I haven't looked at them carefully yet, but I guess that:

* we cannot replace `u"something"` by `b"something"` with Python 2.7, can we?
* I do not want to ignore unicode in doctests related to ascii/unicode, because that's what we are testing!
* I am not sure I want doctests using `six` or some compatibility syntax, because doctests should be easy to understand... but perhaps it is the only way to make the doctests pass...
* perhaps we could have separate doctests for py27 and doctests for py33... but I do not know if it is easy to write, or if it is readable...

> Should we rewrite it in unittest?

The idea would be to explain what users can expect with py27 and with py33. And assert the expectations are met. That's why I'd prefer a doctest than an unittest.

That said, if we cannot find a nice way to do it, we may have a docstring with words (not code) and move the tests in some unittest. But let's try doctest first ;)

> A little help?

Ok, I'll try a few things here :)