Multi-channel hardware support available for testing in Chrome Canary

For those interested in multi-channel output in the Web Audio API, here's
your chance to try out an early build.  This could be of interest for
digital DJ type applications, or rendering to multi-channel speaker
installations...

Please note this is an early build and little testing has yet been made.
 So far I've tested on several devices on OSX.  I'm interested in your
feedback!

The .maxChannelCount attribute is now exposed to show the actual number of
hardware channels:
https://dvcs.w3.org/hg/audio/raw-file/tip/webaudio/specification.html#AudioDestinationNode

The .channelCount attribute should now be settable on the
AudioDestinationNode to values up to .maxChannelCount

Cheers,
Chris