added 3 and 4 op vec2i add

com/danitheskunk/skunkworks/Vec2i.java

@@ -26,6 +26,14 @@ public final class Vec2i {
 		return new Vec2i(a.x + b.x, a.y + b.y);
 	}
 
+	public static Vec2i add(Vec2i a, Vec2i b, Vec2i c) {
+		return new Vec2i(a.x + b.x + c.x, a.y + b.y + c.y);
+	}
+
+	public static Vec2i add(Vec2i a, Vec2i b, Vec2i c, Vec2i d) {
+		return new Vec2i(a.x + b.x + c.x + d.x, a.y + b.y + c.y + d.y);
+	}
+
 	public static Vec2i sub(Vec2i a, Vec2i b) {
 		return new Vec2i(a.x - b.x, a.y - b.y);
 	}