With the Python 2.7 deadline fast approaching, modernize the codebase
making use of the modernize module to switch to using six, as well as
other upcoming features, such as absolute imports . Stop using 2to3
for Travis, yay!
Added support for the traffic endpoints found at https://developer.github.com/v3/repos/traffic/.
We added four functions to the Repository class (one for each of the endpoints) with corresponding unit tests.
Fixes#926
Steve Kowalik