Autocompletion on spaced strings

It seems autocomplete module splits autcomplete elements and use only the last part.

So doing:

```
vorpal.command('cat')
.autocomplete(['foo', 'blah blew']);
```

Would present this list:

`foo blew` instead of showing `foo "blah blew"`

This is especially a problem when using autocomplete-fs module to autocomplete directories since directories containing spaces will be cut out.

Maybe there is an option for that but I didn't see it mentionned in the documentation.