Add PSR-0 and Composer Support

This PR adds Composer support (a composer.json file) as described in #3.

It also adds PSR-0 support so everything will be auto loaded with composer or any other PHP Framework. :)

https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-0.md

You can learn more about PSR standards here:
http://www.php-fig.org/

I decided not to preserve the existing class names, but if you think it's important let me know and I can change it.

Thanks!