Missing code or dependency

TL;DR:
* Add fluent-helloworld as a dependency
* Add maven exec plugin configuration to be able to launch server with mvn exec:java

Long version:
After cloning the project and reading the pom, I was hoping that something along the lines of:

`mvn exec:java -Dexec.mainClass="net.codestory.HelloWorldServer"`

would let me start the main class. Unfortunately this fails with a `ClassNotFoundException`.

In order for this to work, I have to do either one of these 2 things:
* Clone [fluent-helloworld](https://github.com/CodeStory/fluent-helloworld), `mvn install` and add the `net.code-story.empty:1.0-SNAPSHOT` dependency to the pom. (though `empty` is a rather strange name for an artifact so I sent [a PR to rename it to `fluent-helloworld`](https://github.com/CodeStory/fluent-helloworld/pull/1))
* Copy-paste [HelloWorldServer](https://github.com/CodeStory/fluent-helloworld/blob/master/src/main/java/net/codestory/HelloWorldServer.java) into this project.

This PR is for the 1st option, with the added maven exec plugin configuration to be able to start the blog with:
`mvn exec:java`

Hope this is helpful, thanks for this sample.