0.17.0 - 2019-04-12

Add support to HKDF

• Add support to HKDF (HMAC key derivation function).

Misc.

• Change branching model to fast-forward merge on the master branch.
• Change directive language_level from 2 to 3 for Cython.

Bugfixes

• *: Fixup handling of empty and None buffers (#20: Roman (inpos)).
• hmac: Hmac now accepts the empty key (b"").