Support java.time Instant and java.time Clock

[Marthym]

It should be a great thing to be able to support java.time.Instant and java.time.Clock instant of Date and io.jsonwebtoken.Clock.

Jwts.builder()
       .setSubject(user.username())
       .setId(tokenId.toString())
       .setExpiration(Instant.now().plus(expiration))
       .setIssuedAt(Date.from(now))
       .addClaims(claimsBldr.build())
       .signWith(SignatureAlgorithm.HS512, signingKey)
       .compact();

Jwts.parser()
       .setSigningKey(signingKey)
       .setClock(Clock.systemUTC())
       .parseClaimsJws(token.replace(PREFIX, ""))
       .getBody();

[lhazlewood]

This depends on #308

[lhazlewood]

Closing as duplicate of #235. Please #235 for work/discussion.