repository of DOL examples

[mcodescu]

we have https://ontohub.org/repositories/dol-examples, but many of the examples there don't work, because they make use of either a logic/translation not available there, or a DOL construct that is not yet supported in Hets. The idea would be to have a repository where examples can be added only after a pull request, so we make sure that they go through in Hets and they are well-enough documented. Maybe for the examples that don't yet work we could have another repository (of specifications that we would like to be able to write).