Support invalid UTF-8

[tertsdiepraam]

Necessary for uutils-term-grid, see uutils/uutils-term-grid#44.

Quoting from that issue:

There are some combinations of options that require ls to display non-UTF-8 byte sequences in a grid. Because this crate only supports String (and spaces), this isn't currently possible. Support should be added for invalid UTF-8 somehow, accepting one of &[u8], OsStr(ing), or AsRef<OsStr>.

[egmontkob]

Please see my comment at uutils/uutils-term-grid#44.