#23 Add support for Ogg Vorbis encoding

[Olivier Gauwin]

I think it could be interesting to have a support for
ogg encoding (instead of mp3 encoding) in Osmose. The
main reason is that Ogg Vorbis is totally patent-free
and open source.

We could firstly leave the mp3 encoding support and add
a property to choose which encoder the user prefers to use.

This feature is not an emergency, as support for mp3 is
already provided.