Add SHA2 algorithms for HMAC

BUG: https://red.libssh.org/issues/91

Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
Add logic to support SHA2 HMAC algorithms

BUG: https://red.libssh.org/issues/91

Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
Add negotiation for SHA2 HMAC algorithms

BUG: https://red.libssh.org/issues/91

Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
Add options support for setting and getting HMAC algorithms

BUG: https://red.libssh.org/issues/91

Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
Add tests for SHA2 HMAC algorithms

BUG: https://red.libssh.org/issues/91

Reviewed-by: Andreas Schneider <asn@cryptomilk.org>