PHC winner release

[Jean-Philippe Aumasson]

I'm happy to release the Password Hashing Competition winner, Argon2: specs and public-domain code at https://password-hashing.net/#argon2 

Please report any issue with the Argon2 code (as GitHub issues preferably), and let us know if you write bindings for another language

A crypt(3)-like encoding format is specified in https://github.com/P-H-C/phc-string-format/, and will be integrated in the ref code.

Guess this officially closes PHC, so I'd like to thank everyone: designers, panel members, mailing list posters, testers. Hope we'll have done something useful!