Updated Python 3 migration tools and HOWTO guide

[Nick Coghlan]

Brett Cannon recently published an updated version of the Python 3
migration guide: https://docs.python.org/3/howto/pyporting.html

One addition I found particularly noteworthy is the "pylint --py3k"
mode, which is designed to allow a project to keep their own code
"Python 3 ready", even if their dependencies aren't available in
Python 3 yet.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia