PSR-0 compliance

Most PHP libraries are now complying with the PSR-0 standard for autoloader interoperability.
Here is the simplest modification to comply with this standard.

This makes PHP 5.3 the minimum required version; as the current version is 5.4.8, it may be time for this change.

Examples & tests are running ok.

The PSR-0 standard: https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-0.md