Queue multiple files

This is doing a few things

1. Use gemspec to manage dependencies
2. Add rake's gem tasks to facilitate common gem tasks
3. Code I added along the way to be able to queue a list of songs and move through them
4. Added some extra methods, like storing the file name in the Mpg123 instance, and closing the portaudio stream when the bin script exits

Let me know what you think

I'm going to work on the `Curses` visualization for the bin script next, then I would like to be able to scroll through a list of the files you provide to audite (from the bin script viz) and play them as selected. Are these things you're interested in having?