[WIP] Use a Producer-Consumer pattern

This should split up some of the convoluted naming and internal components some more, and give better clearity into how Raekke is working internally.

Plan of Attack
---------------------

A Consumer should be the entry point for a long running process that get messages from a single queue object. For every message it should fork its process and allow the service object invocation to be performed in it. When done it should repeat the process.

A Consumer should listen for normal signal and handle those by sending the signal on to the forked process running a job (if any) or just kill it and mark the job as failed/retry. If no consumer child process is running it should just exit.

The forking could be implemented with Spork from Kris Wallsmith

``` php
<?php

namespace Raekke;
class Consumer {};

namespace Raekke\Consumer;
class Job {};
```