Argon2: Check that a whole number of bytes is requested (#54)

In the Argon2 derive bits operation, throw an `OperationError` if a
number of bits that's not a multiple of 8 is requested.

Author: twiss

index.html

@@ -6882,7 +6882,8 @@ <h5>Derive Bits</h5>
         <ol>
           <li>
             <p>
-              If |length| is null, or is less than 32 (4*8), then [= exception/throw =] an {{OperationError}}.
+              If |length| is null, or is less than 32 (4*8), or is not a multiple of 8,
+              then [= exception/throw =] an {{OperationError}}.
             </p>
           </li>
           <li>