[whatwg] Make Vorbis a baseline codec for <audio>

[Remco]

A few years ago, Vorbis as a baseline codec for <audio> was dismissed,
because it was expected that the audio codec agreed upon to be used
with <video> would also be used with <audio>. Now that agreement on a
codec for <video> is out of the question, Vorbis can again be
considered as a baseline codec for <audio>.

To get the discussion started: a few reasons to require Vorbis for <audio>:

* De facto baseline codec PCM WAV is ridiculous for music and spoken
word - the major use cases of <audio>
* Vorbis is the best lossy audio codec
* Vorbis is widely adopted by major companies in portable media players
* Vorbis is royalty-free

Remco