add select block to button press channel

- outchan is unbuffered, so drop the message if there's already one sitting there.

main.go

@@ -211,7 +211,10 @@ func delayChan(inchan <-chan bool, outchan chan<- bool) {
 		now := time.Now()
 		if now.Sub(last) > pressdelay {
 			last = now
-			outchan <- val
+			select {
+			case outchan <- val:
+			default:
+			}
 		}
 	}
 }