Fix: hearing protection

[ImplicitDeny]

This will fix #33 by adding a balanced hearing protection :

• helmet with no visible protection have no effect on hearing.
• helmet with visible protection have an effect on damage (50% reduction) and perception (30% volume reduction).

Using only earplugs will prevent 75% of damages, but also cause a 50% volume reduction. Best protection is achieved by combining earplugs and protective helmets, since ACE hearing damage protection is cumulative.

In the end :

• no protection : 100% hearing capacity , 0% damage reduction.
• earplugs alone (or with unprotected helmet): 50% hearing capacity, 75% damage reduction.
• protective helmet alone : 70% hearing capacity, but only 50% damage reduction.
• earplugs + protected helmet : only 35% hearing capacity, but almost 88% damage reduction.

[ImplicitDeny]

Note : #6 is apparently something ACE was thinking about (following a discussion with BaerMitUmlaut), but possibilities are very limited in A3. Custom functions and balancing constraints specific to GSRI gameplay might still be a plus.