Composer support

I've set up the repo so it can be used on composer, I was hoping I could leave this pull request active until a later date for reference if anyone looks.

Now, in order to add this to your composer project (inc utilizing the composer autoloader) all you need to do is add "ise/php-soundcloud": "dev-master" to your composer.json (or run composer require ise/php-soundcloud dev-master) in your project root.