Invoke Clingo from Shaclex

[labra]

It would be great that the usage of Clingo inside the validator was transparent, so a user could run the validator and see the results, without having to know that here was a Clingo program running under the hood.

I think there are 3 ways:

• Invoke it as an external process. It would require some configuration variable to point to the Clingo executable, which could be invoked inside Scala using scala.sys.process

• Integrate Clingo inside a Java/Scala program. The asp4j seems to do it but it is not maintained and I think at the end it is invoking Clingo.

• Use a different ASP solver that can be invoked inside a Java/Scala. One possibility could be JDLV or Alpha-ASP.