By default `clap` now automatically wraps and aligns help strings to the
term width. i.e.
```
-o, --option <opt> some really long help
text that should be auto aligned but isn't righ
t now
```
Now looks like this:
```
-o, --option <opt> some really long help
text that should be
auto aligned but isn't
right now
```
The wrapping also respects words, and wraps at spaces so as to not cut
words in the middle.
This requires the `libc` dep which is enabled (by default) with the
`wrap_help` cargo feature flag.
Closes#428
