Add knockback event

src/main/java/net/citizensnpcs/api/event/NPCKnockbackEvent.java

@@ -0,0 +1,44 @@
+package net.citizensnpcs.api.event;
+
+import org.bukkit.event.HandlerList;
+import org.bukkit.util.Vector;
+
+import net.citizensnpcs.api.npc.NPC;
+
+public class NPCKnockbackEvent extends NPCEvent {
+    private double strength;
+    private Vector vector;
+
+    public NPCKnockbackEvent(NPC npc, double impulse, double dx, double dz) {
+        super(npc);
+        this.strength = impulse;
+        this.vector = new Vector(dx, 0, dz);
+    }
+
+    @Override
+    public HandlerList getHandlers() {
+        return handlers;
+    }
+
+    public Vector getKnockbackVector() {
+        return vector;
+    }
+
+    public double getStrength() {
+        return strength;
+    }
+
+    public void setKnockbackVector(Vector vector) {
+        this.vector = vector;
+    }
+
+    public void setStrength(double strength) {
+        this.strength = strength;
+    }
+
+    public static HandlerList getHandlerList() {
+        return handlers;
+    }
+
+    private static final HandlerList handlers = new HandlerList();
+}