Add new position_nudgestack into NAMESPACE

Author: Thomas Knecht

NAMESPACE

@@ -188,6 +188,7 @@ export(PositionIdentity)
 export(PositionJitter)
 export(PositionJitterdodge)
 export(PositionNudge)
+export(PositionNudgeStack)
 export(PositionStack)
 export(Scale)
 export(ScaleContinuous)
@@ -405,6 +406,7 @@ export(position_identity)
 export(position_jitter)
 export(position_jitterdodge)
 export(position_nudge)
+export(position_nudgestack)
 export(position_stack)
 export(qplot)
 export(quickplot)