Refactor the tailer options to use the interface-apply pattern.
Refactor the tailer options to use the interface-apply pattern.

This shortens the code in each option, though the niladic OneShot gets a bit
longer due to its niladness.  I heard a rumour I might be able to stop
double-handling options from mtail.New to here if I try this.

SuperQ/mtail,google/mtail,SuperQ/mtail,google/mtail