updated python 2 vs 3 (fixes #48)

it’s 2014.
i think this paragraph is redundant, as the following one pretty much says the same.

also usually “writing code that works in both Python 2 and Python 3 is **not** a very complicated process.” it’s actually pretty trivial for most small libraries or programs. just import everything from __future__ and create some wrappers around APIs that use bytes on python 2 and strs on python 3, and you’re set. i think the following paragraph serves to explain that.