Python3 Support

[jmatt]

Doesn't work with python3.

In [1]: import threepio
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-1-fe272a3c9349> in <module>()
----> 1 import threepio

/Users/jmatt/.venvs/s3s3/lib/python3.5/site-packages/threepio/__init__.py in <module>()
     23 
     24 VERSION = version.VERSION
---> 25 version = version.get_version(form='verbose')
     26 
     27 LOGGER_NAME = "threepio"

/Users/jmatt/.venvs/s3s3/lib/python3.5/site-packages/threepio/version.py in get_version(form)
     53     if form is "normal":
     54         return v
---> 55     v += " @" + git_sha()
     56     versions["verbose"] = v
     57     if form is "verbose":

TypeError: Can't convert 'bytes' object to str implicitly