Clarify Python version support
Clarify Python version support

Tested Python 3.3 and 3.4 at https://travis-ci.org/hickford/clint/builds/46098963
1gitGrey/clint,wkentaro/clint,1gitGrey/clint,Lh4cKg/clint,tz70s/clint,nathancahill/clint,wkentaro/clint,thusoy/clint,nathancahill/clint,glorizen/clint,kennethreitz/clint