VLCMedia: correctly mark optional delegate protocol parts as such
VLCMedia: correctly mark optional delegate protocol parts as such

siuying/VLCKit,CollabraMusic/VLCKit,waterskier2007/VLCKit,CollabraMusic/VLCKit,siuying/VLCKit,simon1984/test,strukturag/VLCKit,waterskier2007/VLCKit,hpsoar/VLCKit,larrytin/VLCKit,kamcord/VLCKit,programming086/VLCKit,kamcord/VLCKit,strukturag/VLCKit,kamcord/VLCKit,larrytin/VLCKit,simon1984/test,simon1984/test,waterskier2007/VLCKit,programming086/VLCKit,hpsoar/VLCKit,CollabraMusic/VLCKit,siuying/VLCKit