- io('path/to/symlink') would return a file object
if the link was to a file
- $link->readlink incorrectly returned a new IO::All::Link
object, no matter what the link pointed to.
- io($io_all_object) would not return an object of the same
type as the object give to io(), it would always return a
plain IO::All object.
- add head and tail methods
