More quest log documentation amid other stuff

src/sound.c

@@ -193,7 +193,7 @@ void PlayFanfareByFanfareNum(u8 fanfareNum)
 {
     u16 songNum;
 
-    if(gQuestLogState == 2)
+    if(gQuestLogState == QL_STATE_PLAYBACK)
     {
         sFanfareCounter = 0xFF;
     }
@@ -362,7 +362,7 @@ void PlayCry4(u16 species, s8 pan, u8 mode)
 
 void PlayCry7(u16 species, u8 mode) // exclusive to FR/LG
 {
-    if (gQuestLogState != 2 && gQuestLogState != 3)
+    if (!QL_IS_PLAYBACK_STATE)
     {
         m4aMPlayVolumeControl(&gMPlayInfo_BGM, 0xFFFF, 85);
         PlayCryInternal(species, 0, CRY_VOLUME, 10, mode);
@@ -571,7 +571,7 @@ void PlayBGM(u16 songNum)
 
 void PlaySE(u16 songNum)
 {
-    if(gDisableMapMusicChangeOnMapLoad == 0 && gQuestLogState != 2)
+    if(gDisableMapMusicChangeOnMapLoad == 0 && gQuestLogState != QL_STATE_PLAYBACK)
         m4aSongNumStart(songNum);
 }