psound -- priority-aware channel-3-only sfx playback

vacation.p8

@@ -275,6 +275,13 @@ function font_special()
  poke(0x5f58, 0x81)
 end
 
+-- play sound n on channel 3 iff
+-- 3 doesn't already have a
+-- greater index sound going
+function psound(n, off, len)
+ if (stat(49) < n) sfx(n, 3, off, len)
+end
+
 -->8
 -- text rendering