Permit single files on the command line as well as directories
Add Ogg Vorbis support, and fall back to autodetect rather than ID3v2
Fix TXXX support for ID3v2
Implement fallback tags in 'mo sort'

This lets you write {foo/bar} to use foo if set, and bar otherwise.

The default value for --dir-name has been updated to recreate the
old behaviour of {group} using this construct.
README update.
Add disclaimer and Apache license