Add chapter on commandline arguments

Please let me know if you think the example should be more verbose.
Why? It is just a vector, not a function.


2014-06-30 21:11 GMT-04:00 Jorge Aparicio <notifications@github.com>:

> In examples/staging/arg/getopts/echo.rs:
>
> > +        println!("Usage:");
> > +        println!(" {0:s} [SHORT-OPTION]... [STRING]...", program);
> > +        println!(" {0:s} LONG-OPTION", program);
> > +        println!("");
> > +        println(getopts::usage("Echo the STRING(s) to standard output.", opts)
> > +                .as_slice());
> > +        return;
> > +    }
> > +
> > +    if matches.opt_present("version") {
> > +        println!("echo version: {:s}", VERSION);
> > +        return;
> > +    }
> > +
> > +    if !matches.free.is_empty() {
> > +        //^ `matches.free` contains all arguments that are not options.
>
> I think "returns all the arguments that ..." would be more precise.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/japaric/rust-by-example/pull/76/files#r14384987>.
>