Added a -f (--follow) option, but I haven't implemented it yet. I just
don't want to forget this idea. I anticipate that this will be very
useful with log files. For example:

    slice -fd, '/var/log/messages,^Oct 15 09:45:15'

This would, in effect, "tail -f /var/log/messages" beginning with the
first entry from October 15th at 09:45:15.