- update to 3.21.0:
* By setting the PYCRYPTODOME_DISABLE_GMP environment variable,
the GMP library will not be used even if detected.
* Add support for Curve25519 / X25519.
* Add support for Curve448 / X448.
* Add attribute curve to EccPoint and EccXPoint classes, with
the canonical name of the curve.
* GH#781: the label for the SP800_108_Counter KDF may now
contain zero bytes. Thanks to Julien Rische.
* GH#814: RSA keys for PSS can be imported.
* GH#810: fixed negation of Ed25519 points.
* GH#819: accept an RFC5916 ECPrivateKey even if it doesn't
contain any of the optional elements (parameters [0] and
publicKey[1]).
* Remove support for Python 3.5.