Change AMD definition to anonymous module. Close #65.

Change AMD definition to create anonymous module rather than named and
create global objects whether AMD is available or not.
Survive from IE9 throwing "Not implemented"

Apparently IE occasionally throws "Not implemented" from `new Audio()`
Behavior was encountered when runnin IE9 and Windows 7 on Sauce Labs
cloud.  Other reports of this issue relate to Windows Server 2008 or
Windows running in a VM.
Merge remote-tracking branch 'remotes/fsbdev/master'
Updated Howler.js with the playbackRate property in the Howl object

I have added the playbackRate property in the Howl object. I found myself extending Howler with this since I needed it in my game, and because it isn't that much work but a great feature that will hopefully help other people as well,  I thought I'd submit it here in a Pull Request.

The playbackRate is a WebAudio API-only property that enables you to play a sound at a different speed and pitch(useful for games) than normal. It even allows you to play a sound in reverse.
Values are: 1.0 (default) for normal speed, 0.5 for half speed, 2.0 for double, -1.0 for reverse, and so on.
Merge branch 'pr/69'
Merge branch 'pr/73'
Merge branch 'pr/82'

Conflicts:
	howler.js
Bump to v1.1.12