[Toolkit.Audio] Adding audio support to the toolkit.

As requested:

Added new assembly implementing audio support for the toolkit. This is roughly based on XNA and the DirectX toolkit. It is still a work in progress. Pull request for sake of tracking progress.

Known issues:

* Crashes when when reverb is enabled. (Problem has been identified, just needs to be corrected).
* Missing documentation comments.
* Missing nuspec file
* Some code styling issues.