Add chapter on commandline arguments

Please let me know if you think the example should be more verbose.
Windows often uses `/` instead of `-`, and I have never seen long options
there (`--option`). But I haven't done any CLI there either. I think
`getopts` is unix/GNU style.

See [1] and [2].


[1] https://en.wikipedia.org/wiki/Command-line_interface
[2] https://en.wikipedia.org/wiki/Getopt


2014-06-30 21:15 GMT-04:00 Jorge Aparicio <notifications@github.com>:

> In examples/staging/arg/getopts/input.md:
>
> > @@ -0,0 +1,29 @@
> > +To build unix-style command line interfaces, you can use the [getopts](http://doc.rust-lang.org/getopts/index.html) crate.
>
> Just curious, are these interface called "unix-style" for some historical
> reasons? Doesn't windows have similar interfaces? (I've never done any CLI
> development on windows)
>
> —
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> <https://github.com/japaric/rust-by-example/pull/76/files#r14385079>.
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