Use site-maven-plugin to create github mvn-repo branch as repository for...

... jars

When "mvn deploy" is run, jars are pushed to a special branch called "mvn-repo"

To use, you need to configure ~/.m2/settings.xml as follows:

```
<settings>
    <servers>
        <server>
            <id>github</id>
            <username>[your username]</username>
            <password>[your pw]</password>
        </server>
    </servers>
    <properties>
        <my.github.username>[your username]</my.github.username>
    </properties>
</settings>
```