fuse::mount should take a generic AsRef<OsStr> argument

[asomers]

The current signature of fuse::mount requires providing an actual array of &OsStr references. Those are annoying to create, especially from constants. It would be more ergonomic if it could take any argument that implements AsRef<OsStr>. It would look something like this:

pub fn mount<FS: Filesystem, P: AsRef<Path>, O: AsRef<OsStr>>(
    filesystem: FS, 
    mountpoint: &P, 
    options: &[O]
) -> Result<()>