Update sound.coffee

Remove all HTML5 audio tag code in favor of AudioContext API. This greatly reduces the complexity of the Sound class and is potentially far more powerful. Testing is required as soon as possible, and if all goes well support of different audio nodes is the next major goal as far as the Sound class is concerned.
basic sound tests passed

Due to several browsers (primarily IE) not currently supporting the
web audio api, use of the audio tag will have to be included.
Basic background tracks and event driven sounds are up and running.
Inclusion of an easy api to use other audio nodes is a future goal.
include audio tag support

I've tested both the audio tag and web audio api setups and everything
seems to be working correctly. The only thing left to do is add
the gainnode/volume code to allow the user to set/change the volume
add volume control to Sound.play()

basic sound functionality is up and running, this branch is ready to
be merged with master