In OpenSSL 1.1.0, EVP_CIPHER_CTX, HMAC_CTX, and EVP_MD_CTX are opaque types, and have
to be allocated with *_new methods and deallocated with *_free.

EVP_CIPHER_CTX_new/free is present in OpenSSL 1.0.1 and later, but HMAC_CTX_new and
EVP_MD_CTX_new are new in OpenSSL 1.1.0.

Use the _new unconditionally for ciphers, and conditionally use the old or new APIs
for HMAC and MD.

No noticible performance change for older OpenSSL.