Include tests for Clingo encodings

[labra]

At this moment the Clingo encoder generates Clingo programs but is not really tested.

I would like that the encoder could also be tested as part of the continuous integration process, checking that the ouput of the program generated matches the expected output.

I foresee two ways to do it:

• Inside Travis, download Clingo and run it against the generated programs to check that their output conforms with the expected output.

• Integrate Clingo as part of the Scala program and invoke it internally. I would prefer this option because we could make transparent the usage of Clingo to the external user, but it would require to invoke Clingo inside JVM. I looked for some projects that invoke Clingo from Java and found asp4j, but it seems it is not maintained.

At this moment, I don't know yet how to do it, so any help would be appreciated.