In the Python 2 to 3 conversion, the name of the binary type was changed

from str to bytes, and the name of the string type was changed from

unicode to str. In addition, there were some other changes such as

the removal of the basestring type. The six library included a bunch

of helpers to ease this transition. Now that we're Python 3+ only on the

master branch, we can get rid of these and just use the builtins.

Ran unit tests.