Add support for CMAC

[kmfukuda]

Implements #802 by adding the OpenSSL::CMAC class.

The class has a similar set of methods to OpenSSL::HMAC except that

• it calls MACs mac s and that
• it does not have #reset .

The class uses different sets of OpenSSL functions depending on the version that the class is compiled against.

• EVP functions (OpenSSL 3)
• older functions (other versions)