Allow for tag metadata in files/editing from within Django

[emacsen]

mp3s suporrt id3, and vorbis supports comment fields. wav can "kinda sorta" support some of these (http://wavmetadata.blogspot.com/). It would be great if we could edit very common fields such as title and artist, through the django-audiofield, as well as being able to retrieve data such as length (in time) of the file.

[areski]

It might be good if you can provide a pull request with patch to make this possible. Thanks