Python 3 compatibility and version 0.6 bump

There were just a couple little tweaks needed to make things run correctly with Python 3:

*  Fix issue where namedtuple was always the custom function and never the one in collections (because the importerror would always occur even after Python 2.6)
*  Change iteritems to items in one place.

I also took the liberty of bumping things up to version 0.6.