Add initial support for Python 3.x.
Review Request #9330 - Created Oct. 26, 2017 and submitted
This updates kgb to work with both Python 2.x and 3.x. There were a
handful of changes needed to support 3.x, but they mostly amounted to
changes in attributes for functions and classes, the addition of one
more parameter for the
CodeTypeconstructor, and a switch to Unicode
This change does not support keyword-only arguments, which will require
Ran unit tests on Python 2.7 and 3.5.