Make beginMax and endMin optional

Let the user specify only beginMin and endMax, making beginMax and
endMin take the default values beginMin + 1 and endMax - 1 in which
case.

Signed-off-by: Alexander Berntsen <alexander@plaimi.net>
Signed-off-by: Stian Ellingsen <stian@plaimi.net>
Reviewed-by: Stian Ellingsen <stian@plaimi.net>