poly1305 message authentication code go library

 Poly1305 is a fast, one-time authentication function created by Daniel
 J. Bernstein. It is infeasible for an attacker to generate an
 authenticator for a message without the key. However, a key must only
 be used for a single message. Authenticating two different messages with
 the same key allows an attacker to forge authenticators for other
 messages with the same key.