Add a sound driver.
Make the sound driver work.
- address issues that came up in the pull request
- fix bugs found with further testing
- make it possible to have a callback function when the sound stops
- Declare some variables used in the case statement which got missed the first time around.
- correct capitalization in an error message.
- Some final changes based on Brett's merge comments.
Merge pull request #202 from virtual-world-framework/sound-driver

Add a sound driver.