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

Author: d-e-s-o

src/help.rs

@@ -71,22 +71,22 @@ pub fn wrap_text(buf: &mut Write, data: &str, width: usize, indent: usize)
             return Ok(());
         }
         Some(word) => {
-            try!(buf.write(word.as_bytes()));
+            try!(buf.write_all(word.as_bytes()));
             off += word.len();
         }
     }
     for word in witer {
         if off + word.len() + 1 > width {
-            try!(buf.write(b"\n"));
+            try!(buf.write_all(b"\n"));
             for _ in 0..indent {
-                try!(buf.write(b" "));
+                try!(buf.write_all(b" "));
             }
             off = indent;
         } else {
-            try!(buf.write(b" "));
+            try!(buf.write_all(b" "));
             off += 1;
         }
-        try!(buf.write(word.as_bytes()));
+        try!(buf.write_all(word.as_bytes()));
         off += word.len();
     }
     return Ok(());