Add composer support

This PR breaks BC :cry:.  I will totally understand if it is denied :ok: 

- Moves class to their on files supporting [PSR-0](https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-0.md) convention (using [namespaces](http://php.net/namespaces))
- Add more targets to the `Makefile`, supporting composer installation

If you are willing to accept this PR, I can update the examples in order to work with composer usage also.