** Added support for Python 3.3+.
** utils.rand_bytes() now sources bytes from os.urandom().
** utils.websafe_encode() now returns text strings (unicode() on Python 2.x,
str() on Python 3.x).
** utils.H() has been removed (just use hashlib.sha256() directly instead).
** soft.SoftU2FDevice() now stores keys, key handles and app params as text
strings.
** Replace M2Crypto with Cryptography.