They say `HMAC' API is deprecated since 3.0, thus `EVP_MAC' API should
be used.
  https://www.openssl.org/docs/manmaster/man3/HMAC_CTX_free.html

- CTR vector is from standard.
- CBC vector is generated by PR_GOSTR_bch_v9. CBC test fail in-place
  decryption, so it's disabled by `#if 0'.

It's 4, half of block size.

From GOST R 34.13-2015 (А.2.6).

From RFC 7836 (B) and R 50.1.113-2016 (A).

Dumps from `etalon/' dir.

Here is better place, because they all digests.

- Use EVP API instead of direct calls to gost-engine;
- Remove MAC tests (they should go into test_digest);
- Expand `testcases' array to be more readable;
- Add some asserts of IV and block sizes.
- Remove noisy hex dumps if there is no errors;
- Note: no new cipers are added.

Better name to add more ciphers to test. Also, move it up in the tests
just after digests.

Test if copying `EVP_MD_CTX' is working good for GOST digests.

Also, use testcases table and add more ciphers.

* Tests that gost-engine correctly computes the public key from the
private key. (Twice -- Alice and Bob.)

* Tests that gost-engine correctly computes the derived shared key.
(Twice -- Alice and Bob, should be identical.)