Provide a source and javadoc artifacts

[stadler]

Add maven sources plugin, update maven javadoc plugin and drop obsolete JVM parameter

Fixes #19

[wbadam]

Hi, thank you for the pull request.

I've eventually used the maven release plugin to create the correct files which was included in the Viritin archetype, just wasn't used before.

If you think it still makes sense to include javadoc and source plugins as part of the normal build process (it might), it should be investigated if these and the release plugin collide in any way.

[stadler]

Hi
I think the sources and javadoc makes still sense, as users of your library will be able to see the actual sources and/or javadoc. So it does not collide but rather complement the release process.
I changed those plugins to be only part of the release process.
I also adapted the javadoc plugin to not fail the build if there are javadoc problems.