** Major release: Changed backend from M2Crypto to cryptography
** Added support for Python 3.3+ and PyPy 2.6+
** Added support for reading transport information from attestation
certificates, as well as metadata statements.
** Added dependency on cryptography 1.2 or higher
** Added dependency on enum34 on python versions < 3.4
** Removed dependency on M2Crypto, pyasn1, and pyasn1-modules
** utils.rand_bytes() now sources bytes from os.urandom()
** utils.websafe_encode(), u2f_v2.RawRegistrationResponse.serialize(),
and u2f_v2.RawAuthenticationResponse.serialize() now all return
text strings (unicode() on Python 2.x, str() on Python 3.x)