Release 0.3.0

Added

• Add sensorStart and sensorEnd to support sensors explicitly indicating
  whether they are active or not. Note that only one sensor can be considered
  active at a time.

Changed

• Activate sensor in createPointerSensor if the pointer has moved more than 10
  pixels. This is irrespective of whether the delay condition has been met. It
  addresses the issue where a dragged item appears to jump to its new location
  after a delay if the pointer moved quickly at the outset of the drag.

• Make managing sensor active state explicit. Returning a truthy value from a
  sensor activator will no longer cause that sensor to be automatically marked
  as the active sensor. In addition, other activators will continue to be called
  until a sensor explicitly indicates it is active by calling sensorStart.
  Similarly, an active sensor must now call sensorEnd when it is no longer
  active (typically when a drag completes). This makes it clearer that a sensor
  is responsible for managing its activation state (and how to do so),
  especially in cases of delayed activation.