support for sfxr data string

Hi,

I add support to play sfxr data string as clip. The data string is injected via url of the clip.

* I did a basic/stupid port from https://github.com/mneubrand/jsfxr, I thinks there are bugs.
* I tested only on Dartium via audio.html (webaudio doesn't with sound driver OSS on chromium or Firefox).

Can you review ?