Serbian translations update.

Hey Pahimar. :D
I improved the Serbian localization file by improving the (obviously Google Translate) translations, adding in the missing stuff (using the en_US file as a reference), and switching it from Cirilic Serbian writing (Russian-like) to Latin Serbian writing (English-like), witch looks better on computers (Mojang derped and mixed them up in vanilla minecraft, so it really doesn't matter witch one mods use.).