yubico.py: Convert key to byte string before passing it to b64decode

In Python3 <= 3.2, the base64.b64decode function only accepts byte strings, so
we need to convert the key to one.
modhex: Use __future__.unicode_literals instead of explicit unicode literals

Makes modhex.py usable with Python3 <= 3.2
Fix lint.
Merge pull request #22 from soult/py30_31_32

Library does not work with Python3 <= 3.2
Fix lint.
Update CHANGES.
query string's values must be quoted/unquoted when splitting-sorting-reconstructing.