sad: introduce nettle mac library Four Message Authentication Code (MAC) libraries will be added: 1. nettle (this patch) 2. gnutls 3. gnupg 4. openssl This patch introduces the nettle mac library along with all functions required including initialization/deinitialization of mac context using key data and generating the digest/mac/icv Signed-off-by: Clay Kaiser <Clay.Kaiser@ibm.com> Reviewed-by: Erez Geva <ErezGeva2@gmail.com> Reviewed-by: Miroslav Lichvar <mlichvar@redhat.com>