Python 3 compatibility

[jmgirven]

This commit takes the current version and makes it compatible with Python 3 (#85). Nothing too complicated. 2to3 does most of the work.

There are no major changes in apns.py, just syntax and explicitly made some parts of the codes bytes to compatible across 2 and 3.

Similar in tests.py. Only line 191-193 needed a small change to account for different ordered dictionaries. An alternative could be test the beginning of the line, the end of the line, and json parse the middle and compare.

[jimhorng]

to make code py3 compatible is good, however, it's better to keep py2 function's behavior when running by py2, for example xrange(), if you turn xrange() into range() which becomes a list instead of iterator, that will harm resource consumption and performance.
Maybe you can take reference from cheetsheet
use pip install future

# Python 2 and 3: backward-compatible
from past.builtins import xrange
for i in xrange(10**8):
    ...

[ExplodingCabbage]

@jimhorng I don't think the range vs xrange performance difference is worth caring about here. We're talking about sometimes creating a list of 10 integers when you otherwise wouldn't have to. That really, really doesn't matter in the grand scheme of things; it's not worth adding any complexity to the code just to avoid creating a list of 10 ints.

[jimhorng]

@ExplodingCabbage agreed +1