Pm pln

Basic infrastructure for implementation of Attentional Focus filtering inside the the pattern matcher.the preliminary implementation of the callbacks could be changed later. one can use the specific implementation by invoking **cog-bind-pln**  from scheme.
> But one question thats in my mind is, Isn't there a scenario that we may need all the matches in the AF regardless of their selection probability?

@misganagit At what step (and where) will that stochastic selection occur? The answer to that question may also impact your last question. Depending on where it occurs, it might be a consumer of such a method; however, I'm not sure what structure you have in mind.