Added comment about py2k py3k. For the record: 2to3 did not find anything I should fix.
Added comment about py2k py3k. For the record: 2to3 did not find anything I should fix.

blink1073/imageio,kuchi/imageio,imageio/imageio,patricksnape/imageio,almarklein/imageio,almarklein/imageio