Refactor to use better interfaces and event callbacks.

elements/mover.go

@@ -114,7 +114,7 @@ func (m *Mover) Draw() {
 	}
 }
 
-func (m *Mover) Update() {
+func (m *Mover) Update() error {
 	/*
 		dx := 0. //40 * math.Cos(float64(m.cycles)/16)
 		dy := 0. //40 * math.Sin(float64(m.cycles)/16)
@@ -130,6 +130,7 @@ func (m *Mover) Update() {
 		m.dyingcount++
 	}
 	m.cycles++
+	return nil
 }
 
 func (m *Mover) SetHit() {