add Korean lyric scrapers: Alsong, GomAudio

add Korean lyric scrapers are added under lib/scraper directory.
In correspondence, two entries are added in settings.xml.

These sites don't use song title & artist name. Instead, hash key should be generated from audio stream, and this key is used to fetch a proper lyric.
Unfortunately, header in audio file should be decoded to determine position of audio stream.
I put these things in one common file, audiofile.py.
I wonder where is the best place to this file. I placed it in lib directory temporally.

These scrapers are programmed two years ago for LRC Lyrics addon.
While I ported them for this addon, I found files which do similar job under tagger directory. But they are focused on extracting title, artist names.
Instead of modifying them, I sent my original file.