1.2.0

Add flag to override the transition duration.

• e. g. -transitionDuration 1h20m
• natural twilight is approximately between 20m and 1h15m at equator,
  but depends on latitude, altitude, objects blocking horizon and time
  of year. The default 1h should work for most people, but adjusting
  should still be possible. Feedback from users in the arctic greatly
  appreciated.