libsodium doesn't have PBKDF2 so derive_key() does nothing for now.
aes_256_cbc probably not needed with sodium.
Replace aes_128_gcm stream cipher with xsalsa20.
Bignum stuff is not in sodium.
PRNG check not in sodium.
Drop libssl rsa and dsa sign keys.
Add sign key but no use it yet (edwards was experimental).
Drop mac test case (no separate mac).
Use type which doesn't depend on openssl defines.
Replace hashing test with more specific digests tests.