Metadata editing/writing

[bcomnes]

Ideally we can use taglib for this. Mafintosh said writing good async bindings for taglib would be harder than writing your own metadata parsing/serializing libs, but maybe we can get away with using some existing bindings:

• taglib
• node-taglib2

The other major side of this project is a good editing interface, and multi-file editing. This is a massive project that would pick up a lot of liability on our end. Probably want to push this out as long as possible.