New version

[tmilos]

• Bump min php version to 5.5
• Move to PSR-4
• Move from JoseJwt namespace to Tmilos\JoseJwt
• Change tests namespace to Tests\Tmilos\JoseJwt
• Add JWE::header(string $token) to read header before decryption
• Add suggest in composer.json for spomky-labs/aes-key-wrap