Add support for php via composer

[nubs]

Composer's composer.json could be used to generate a Dockerfile very similar to Node.js.

[nubs]

I have not seen many projects take advantage of scripts in composer, but that could be a possibility. Otherwise something similar to some heroku buildpacks which use the extra section to define things like docroot and the front controller in order to setup a vhost in apache/nginx/etc. could work well.