Fix clippy reported problems of unused_io_amount lint
Fix clippy reported problems of unused_io_amount lint

This change fixes occurrences flagged by the clippy lint
`unused_io_amount`. E.g.,

> warning: handle written amount returned or use `Write::write_all` instead
>   --> src/help.rs:74:13
>    |
> 74 |             try!(buf.write(word.as_bytes()));
>    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>    |
>    = note: #[warn(clippy::unused_io_amount)] on by default
>    = help: for further information visit
>      https://rust-lang-nursery.github.io/rust-clippy/master/index.html#unused_io_amount

tailhook/rust-argparse