Publish multiplatform metadata

[jcornaz]

When using kwik in a multiplatform project one has to import every target depedencies:

• In common source-set: kwik-core-common
• In JVM source-set: kwik-core-jvm
• In Linux source-set: kwik-core-linux
• Etc.

But it is now possible to publish the metadata in the core artifact so that a multplatform project would only need to make the common source-set to depend on kwik-core in order to get all platform artifacts.

For that I would have to use maven-publish instead of the bintray plugin.

More info: https://kotlinlang.org/docs/reference/mpp-publish-lib.html#publish-a-multiplatform-library