[Rd] Rust bindings to nmath

[Richard Dodd]

Thanks for the feedback!

> Any chance you could rename it to a more neutral r_mathlib or something?
> As a free-standing C library it has long been wrapped by other languages, but
> if it were my project I'd be more careful to not imply "all of stats" here.
> FWIW in Debian we call it `r-mathlib`.

I will rename it to `r-mathlib`. In addition to a more clear name, it
will aid discoverability for users if it has the same name as the same
thing somewhere else. Thanks for the tip.

Rich