Syllogism demo

Initial pull request for testing syllogisms. Work in progress. Not to be merged yet. Comments welcome.
It's good practice to keep code that interacts via a client API separate from code that accesses an internal API directly. I suggest moving this functionality to the https://github.com/opencog/external-tools repository since this depends on that client. (But it is a bit confusing, now that I think of it, to put highly relevant tests, somewhere else... any ideas are welcome.)

I'm glad that you produced this load_r2l script. Do you think it would be feasible to extend it so that it can perform the entire demonstration (including PLN), using the client API?