Refactored the volume processing routine, spawning a single thread responsible of updating the volume.
This solves the problem of competing threads lowering and rising the volume alternatively.
Deafening effect is increased.
Take into account if earplugs from X39 MedSys are present. If X39 is not running or earplugs are not placed the sound strength is unaltered.
Merge pull request #89 from esteldunedain/master

AGM_Hearing: Refactoring of the volume processing routine and support for earplugs