Update examples to not require 2to3 to run under Python 3.

[hodgestar]

The examples folder still requires 2to3, and Genshi no longer uses that so we should update them to run under Python 2 and 3 from a single codebase, using six if necessary.

It's possible that kid doesn't support Python 3 at all, in which case some of the benchmarks against kid will need some other solution.

[a-detiste]

2to3 is removed from Python3.13