Add optional List<int> param to Hash.digest for easier one-liner

Suggesting adding an optional List&lt;int&gt; param to Hash.digest() for the more simple one-liner cases.

Instead of:

var digest = sha256.update(&quot;message&quot;.charCodes()).digest();

It would be nicer to have:

var digest = sha256.digest(&quot;message&quot;.charCodes());

Thanks!
