Rust updates

[Stefan Scholl]

"bearophile" <bearophileHUGS at lycos.com> wrote:

> On default in Rust types are immutable. If you want the mutable type you
> need to annotate it with "mut" in some way.
> 
> Rust designers seems to love really short keywords, this is in my opinion
> a bit silly. On the other hand in D you have keywords like "immutable"
> that are rather long to type. So I prefer a mid way between those two.

Short keywords are only important with barebones editors like a default vi.
Nobody would use this for real development.