1st draft of complete class-based std.random successor

[bearophile]

Joseph Rushton Wakeling:

> I think the following patch should fix that for you:
> https://github.com/WebDrake/std.random2/commit/fb5429de77b3c1f7fe3968fd0bd92209c9021f31
>
> I've also made shuffle composable as per your request.  Looks 
> good? :-)

Seems good. Onward! :-)

Bye,
bearophile