Improve audibility of sounds

It's solution for missing hit/shot/etc. sounds:
1. decrease priority of ambient sounds to low, in order to hear more
non-ambient sounds with priority greater than low;
2. increase amount of sound channels to hear more sounds. Newer sound
cards on PC should be able to use more channels than only 32;
3. improve preset sound settings.

Remark: after these changes for default value of mapsoundrefresh (10)
break in playing ambient sounds, caused by playing sounds with greater
priority, isn't practically audible. The break is audible for greater
value, for example for mapsoundrefresh=1000.

config/menus_settings.cfg

@@ -217,20 +217,20 @@ const new_gfx_quality [
 const new_sound_quality [
   if (= $arg1 3) [ // high sound (DEFAULT)
     soundqualityalias = 3
-    maxsoundsatonce 10
+    maxsoundsatonce (getvarrange default maxsoundsatonce)
     footsteps 1
     bulletairsound 1
     bulletbouncesound 1
   ] [
     if (= $arg1 2) [ // medium
       soundqualityalias = 2
-      maxsoundsatonce 8
+      maxsoundsatonce (div (getvarrange default maxsoundsatonce) 2)
       footsteps 1
       bulletairsound 0
       bulletbouncesound 1
     ] [ // low
       soundqualityalias = 1
-      maxsoundsatonce 5
+      maxsoundsatonce (div (getvarrange default maxsoundsatonce) 4)
       footsteps 0
       bulletairsound 0
       bulletbouncesound 0

source/src/audiomanager.cpp

@@ -622,7 +622,7 @@ void audiomanager::updateaudio()
 
             if(hearable && !loc) // play
             {
-                _playsound(sound, entref, SP_HIGH, 0.0f, true);
+                _playsound(sound, entref, SP_LOW, 0.0f, true);
             }
             else if(!hearable && loc) // stop
             {
@@ -803,9 +803,9 @@ COMMANDF(mapsoundreset, "", ()
     flagmapconfigchange();
 });
 
-VARF(soundchannels, 4, 32, 1024, audiomgr.setchannels(soundchannels); );
+VARF(soundchannels, 4, 128, 1024, audiomgr.setchannels(soundchannels));
 
-VARFP(soundvol, 0, 128, 255, audiomgr.setlistenervol(soundvol); );
+VARFP(soundvol, 0, 128, 255, audiomgr.setlistenervol(soundvol));
 
 COMMANDF(registersound, "siii", (char *name, int *vol, int *loop, int *audibleradius)
 {