[theora] Http adaptive streaming for html5

[Chris Double]

I'm not sold on the approach of listing the different bitrate versions 
in source elements. This will cause issues if the source elements have 
different codecs, sizes, or other characteristics. It also makes it hard 
to know which is a 'fallback' source and which is a bitrate source.

I much prefer the approach of treating bitrate switching as a new codec. 
Have a file on the server that lists the different bitrate versions. 
Much like Apple's live streaming draft RFC.

In this way browsers can support it by implementing the 'codec' and the 
WHATWG doesn't need to be involved at all as far as I can tell.

Chris.