RSA and OpenID Connect support

This is a major release with new features and breaking changes:

New features

Along with HMAC signed tokens, now you can:

• verify RSA signed tokens, validated against a keystore containing a valid public key.
• verify OpenID Connect ID Tokens, validated against public keys downloaded from a valid JWKS uri.

Breaking changes

• upgrade Java version to 8
• JwtTokenVerifier: changed package and removed some methods in favour of JwtAdapter
• JwtTokenBuilder: removed some methods
• JwtTokenValve: now is abstract. You can choose between two implementations: HmacJwtTokenValve (compatible with previous version) and RsaJwtTokenValve, depending on your signing method