WIP. Doesn't work in IE
WIP2
Set defaultPlaybackRate to fix IE behavior
Adds doc/playbackrate.text
Update doc/playbackrate.text
Set playbackRate on the audio-element during the timeout-event
Add an explanation to setPlaybackRate as to why the value isn't set in that function anymore.
Only set playbackrate on browsers that support it.
Move timeupdate-event to a Modernizr.on 'playbackrate' event
Merge pull request #667 from m-abs/playbackrate-fix

Playbackrate fix