Standardise artifacts format

- You should almost never use an appendix on your atifacts, this becomes clear when you start using maven.
- APIs, even the source are normally distributed in jar files, like it is here. I can change this back if you think it is important.
- If you include a jar named "sources" with the full source of a project, IDEs can pick this up and make the source available if you are using maven.
Merge pull request #83 from RX14/gradle-artifacts

Standardise artifacts format