Changing beam knee gap

Kneed beams are inserted automatically when a large gap is detected between the note heads. This behavior can be tuned through the auto-knee-gap property. A kneed beam is drawn if the gap is larger than the value of auto-knee-gap plus the width of the beam object (which depends on the duration of the notes and the slope of the beam). By default auto-knee-gap is set to 5.5 staff spaces.