audio: Tweak mute docs, fix set_mute() return type if no mixer_track
audio: Tweak mute docs, fix set_mute() return type if no mixer_track

quartz55/mopidy,SuperStarPL/mopidy,bencevans/mopidy,tkem/mopidy,mopidy/mopidy,abarisain/mopidy,swak/mopidy,woutervanwijk/mopidy,abarisain/mopidy,jodal/mopidy,jmarsik/mopidy,priestd09/mopidy,hkariti/mopidy,jcass77/mopidy,mokieyue/mopidy,tkem/mopidy,mokieyue/mopidy,dbrgn/mopidy,SuperStarPL/mopidy,jcass77/mopidy,priestd09/mopidy,ZenithDK/mopidy,quartz55/mopidy,jcass77/mopidy,vrs01/mopidy,mopidy/mopidy,bencevans/mopidy,adamcik/mopidy,liamw9534/mopidy,swak/mopidy,adamcik/mopidy,jodal/mopidy,rawdlite/mopidy,glogiotatidis/mopidy,hkariti/mopidy,dbrgn/mopidy,SuperStarPL/mopidy,vrs01/mopidy,jodal/mopidy,jmarsik/mopidy,pacificIT/mopidy,bacontext/mopidy,ali/mopidy,vrs01/mopidy,mopidy/mopidy,kingosticks/mopidy,tkem/mopidy,dbrgn/mopidy,bacontext/mopidy,woutervanwijk/mopidy,swak/mopidy,ali/mopidy,mokieyue/mopidy,ali/mopidy,diandiankan/mopidy,diandiankan/mopidy,glogiotatidis/mopidy,SuperStarPL/mopidy,liamw9534/mopidy,quartz55/mopidy,glogiotatidis/mopidy,diandiankan/mopidy,kingosticks/mopidy,hkariti/mopidy,mokieyue/mopidy,ZenithDK/mopidy,ali/mopidy,vrs01/mopidy,rawdlite/mopidy,ZenithDK/mopidy,dbrgn/mopidy,quartz55/mopidy,rawdlite/mopidy,kingosticks/mopidy,priestd09/mopidy,glogiotatidis/mopidy,hkariti/mopidy,pacificIT/mopidy,swak/mopidy,bencevans/mopidy,bencevans/mopidy,pacificIT/mopidy,pacificIT/mopidy,rawdlite/mopidy,jmarsik/mopidy,tkem/mopidy,bacontext/mopidy,diandiankan/mopidy,adamcik/mopidy,jmarsik/mopidy,bacontext/mopidy,ZenithDK/mopidy