Syllogism demo

Initial pull request for testing syllogisms. Work in progress. Not to be merged yet. Comments welcome.
The BindLink construct is a clear representation. 

> I'm not sure how to designate an arbitrary number of arguments with the PM.

I'm not sure. It reminds me of a related topic that came up for me:
http://wiki.opencog.org/w/Idea:_Recursive_Unification_using_the_Pattern_Matcher