create slice with capacity, when capacity is known

This reduces the number of allocations made to the underlying array, while append() attempts to 'grow' the slice beyond its initial capacity

play.go

@@ -79,10 +79,8 @@ func (r *Recorder) Events() ([]Event, error) {
 
 	events := sortedMerge(evOut, evErr)
 
-	var (
-		out []Event
-		now = epoch
-	)
+	now := epoch
+	out := make([]Event, 0, len(events))
 
 	for _, e := range events {
 		delay := e.time.Sub(now)