Release 0.7.1

Added

• Emit more useful warnings when attempting to remove nonexistent items. Rather
  than fail with error (Cannot read properties of undefined), emit an
  appropriate console warning instead and then return.

Fixed

• Ensure layouts recomputed before other effects on drag start. Without this,
  issues could occur where collisions were detected against stale positions and
  items moved incorrectly as a result. In addition, layouts might not have been
  recomputed correctly on drag end if adjustments were made by custom
  onDragEnd handlers. Now, core behaviour such as recomputeLayouts and
  detectCollisions is called explicitly as part of dragStart and dragEnd
  to ensure correct ordering.

• Don't apply redundant adjustment transformer when a drag overlay is used.

• Improve typings for DragOverlay to better describe function form.