Expose block sizes of block ciphers.

Both via static data members and Encryptor/Decryptor interfaces.
Crucial for safe memory allocation routine.

Chaos/Cipher/Block/Encryptor.hpp

@@ -20,6 +20,11 @@ public:
         return Impl().EncryptBlock(block);
     }
 
+    auto GetBlockSize()
+    {
+        return Impl().GetBlockSize();
+    }
+
 protected:
     Encryptor() = default;