Implement an Answer Set Programming solution

[labra]

The SLang module contains an implementation of the S-Lang defined in this paper which can been implemented by converting the validation to a clingo program.

It encodes the schema, the data and the shape maps as a Clingo program which can externally be solved by Clingo. The converter from SLang to Clingo is implemented in this file.

This feature and encoding is still experimental and we would like to obtain more feedback from users interested in this approach.