python3 support

This is based on my update-ci branch.

See the diff here:
https://github.com/bukzor/python-clom/compare/bukzor:buck-ci-update...bukzor:buck-py3
Why `seq`: I've put this documentation under test, so I needed the output to be reproducible.
The `ls` and `git` commands depended on un-fixtured data, so there was no reliable way to make the doctest pass.

I could look at making a filesytem-fixture for this stuff, but it would be some work.

The bigger question in my mind is: To what extent do you object to the `#doctest:` comments below?
Livable?

Are you available on irc at all?
I'll be working on this a bit more today.