namespace (Patchwork\) and convert to PSR-4 (fixes #11)

Previously JSqueeze claimed PSR-0 compliance in composer.json but was not in fact compliant, as PSR-0 requires at least one level of namespacing, bare classes are not PSR-0 compliant. As PSR-4 has now deprecated PSR-0, convert to PSR-4 while we're about it, which has the handy bonus of meaning the class file does not need to be moved at all.

This is an obvious BC break: all consumers have to switch from calling `new \JSqueeze()` to `new \Patchwork\JSqueeze()`.

My erstwhile colleague Remi Collet contends the namespace should be Patchwork\Jsqueeze , I don't really care, I just want to cry myself to sleep at this point.