Support for PHP source directory

Carsten,

This is a great package. Been using it for a while on my [PHPFUI](http://phpfui.com/?n=cebe%5Cmarkdown&c=Markdown) site which easily documents any PHP code.

I was wondering if you would be up for a Pull Request to put the PHP source in it's own directory. This is pretty standard practice for PHP libraries. I would be willing to submit one, I just don't want to do the work if you have a reason to keep it the way it is. I would go with either PSR-4 or PSR-0 autoloading depending on if you have a preference.

This should not affect any user of the package if they are using composer to install it. The reason I am interested in a dedicated source directly is my PHPFUI site does not use composer for deployment, but has everything checked in. I have a script that copies over files, but it can't easily distinguish between test code and package code. It is also a good logical separation in general.

Anyway, let me know if you think this would be a good idea. Happy to contribute to this excellent project.

Bruce