Syllogism demo

Initial pull request for testing syllogisms. Work in progress. Not to be merged yet. Comments welcome.
If the reasoning is done in the CogServer, I think this could be done by getting the incoming set of the ```(PredicateNode "inputs)```, walking to the EvaluationLink and from there to the ListLink and retrieving its arguments. I haven't done much with hypergraph-walking directly in the atomspace but I figure this shouldn't be too hard.
This should be possible with the PM as well by specifying a BindLink such as the following:
```
(BindLink
    (VariableNode "$var")
    (ImplicationLink
        (EvaluationLink
            (PredicateNode "inputs")
            (ListLink
                (VariableNode "$var")))
        (VariableNode "$var"))
```
though I'm not sure how to designate an arbitrary number of arguments with the PM.