Add instance Random Natural - #73

Dammit, I was sure I fixed that CPP stuff. It probably happened in some PR that never got merged. Oh well, I am really glad you noticed it.

There was discussion about Random instance for Natrual in #44 I was really on the edge of not defining this instance and even closed that issue, but since you already implemented it, I am OK with it to be included. After all that is exactly what Random class is for. 👍

Let's give it a day or so for someone to object, and we can merge it if no-one speaks up.

Same comment as here: #72 (review) - I don't think we should be adding features to Random at this point. There already is a UniformRange Natural instance. If anybody wants to generate Natural values in the Word range, they can already do it.

I don't think we should add this. If someone wants to generate random values for Natural then they should use UniformRange.