Add stopSong

Engine/src/shared/audio.ts

@@ -90,6 +90,12 @@ export function playSong(name: string) {
   }
 }
 
+export function stopSong() {
+  if (playingSongAudio && !playingSongAudio.paused) {
+    playingSongAudio.pause()
+  }
+}
+
 export function playSound(name: string, volume: number): HTMLAudioElement|undefined {
   if (!enabled) return
   let s = audioCache.pop()