remove demo game

util.timer.go

@@ -0,0 +1,10 @@
+package pncdsl
+
+// Timer accumulates seconds. Tick advances it; Reset zeroes it.
+type Timer struct {
+	Elapsed float64
+}
+
+func (t *Timer) Tick(dt float64) { t.Elapsed += dt }
+func (t *Timer) Reset()           { t.Elapsed = 0 }
+func (t *Timer) Done(after float64) bool { return t.Elapsed >= after }