Metalparser

- Solved bug causing an incorrect download of albums' release year;
- General improvements in stability;

The library comes (at the moment) with 6 APIs:

- get_artists_list()
- get_albums_info()
- get_songs_info()
- get_album_info_and_lyrics()
- get_albums_info_and_lyrics_by_artist()
- get_song_info_and_lyrics()