Unsigned hash object properties

[twoeths]

Motivation
This is the way we calculate a HashObject from byte array:

as-sha256/src/index.js

Line 92 in d2b3c07

return byteArrayToHashObject(staticInstance.uint8OutputArray);

The result may return negative numbers, we want to make it unsigned integers to be more clean, make sure we don't have any performance impact with that.