#97 ID3v2 additions + %N (number of tracks) switch (3.1.1)

[Jeff Mahoney]

This patch does a couple of things, mostly related to
ID3v2 tags. It
adds the "Composer" frame to ID3v2 output, changes the
track number output for ID3v2 to #/#, so that the
number of tracks on the CD is available, and adds a
"%N" replacement field that expands to the number of
tracks on the disc. The ID3v2 changes conform with
ID3v2 standards, and are extremely useful for owners of
portable MP3 players, such as the iPod.

This is fairly straightforward, except that I chose to
pass ID3v2TagFile() an EncodeTrack rather than 8
separate arguments. This is done because 1) I think
it's cleaner, and more importantly, 2) because ID3v2
offers a huge number of frame types, and it's easier to
add support for them with all the data available.

[Jeff Mahoney]

ID3v2 additions against 3.1.1