Support files with ID3V2 tags

[alza-bitz]

If a file contains ID3V2 tag, skip it and parse the mp3/xing/lame headers with the relevant offset, to skip the ID3V2 tag.

See http://fileformats.archiveteam.org/wiki/ID3#How_to_skip_past_an_ID3v2_segment for a rough outline of how to skip past the tag..