Range-based streaming, seeking

Currently may explode if no range support. :)

* StreamFile majorly refactored
* -> supports seeking: https://github.com/brion/ogv.js/issues/123
* -> uses smaller buffer chunks: https://github.com/brion/ogv.js/issues/125
* Basic bisect seek supported for theora, vorbis
* AudioFeeder refactored to support stop/start and seeking
* Audio now shuts down when paused: https://github.com/brion/ogv.js/issues/78

Some issues:
* No fallback for non-Range-handling stuff
* Issues a separate HEAD request to get the content-length;
  ideally this should use the Content-Range but that has to
  be separately whitelisted on the server. Seriously?
* Seek doesn't properly detect all packet timestamps and may
  not always go to right keyframe. Will replace all this with
  liboggz in a bit anyway.