LibCrypto: Implement HMAC

Author: https://github.com/alimpfard
Commit: f2cd004d11
Pull-request: https://github.com/SerenityOS/serenity/pull/1661
Reviewed-by: https://github.com/Dexesttp
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/itamar8910

Libraries/LibCrypto/Hash/HashFunction.h

@@ -49,6 +49,7 @@ namespace Hash {
         virtual void update(const StringView& string) = 0;
 
         virtual DigestType digest() = 0;
+        virtual String class_name() const = 0;
     };
 }
 }