FIX #443 Refactor documentation. Work in progress

A preview is available. Currently done

- [landing page](http://mukis.de/sbt-native-packager/)
- [debian plugin](http://mukis.de/sbt-native-packager/formats/debian.html)
- [rpm plugin](http://mukis.de/sbt-native-packager/formats/rpm.html)
- [docker plugin](http://mukis.de/sbt-native-packager/formats/docker.html]

partially done

- [linux plugin](http://mukis.de/sbt-native-packager/formats/linux.html)