Python 3 compatibility and version 0.6 bump

[dan-blanchard]

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.

[davidr]

Awesome, and thanks! I'll test it out early next week and merge it in.

[dan-blanchard]

Hi, I don't mean to be a pest, but this prevents our package, gridmap, from working on Python 3, so if you could merge this, I'd really appreciate it.

[davidr]

Thanks for the update. I'm a fool and forgot about it. Merging it now.

[davidr]

It has also been uploaded to PyPI. Thanks very much for your extended patience.

[dan-blanchard]

Thanks!