Add %likely/%unlikely variables

[jrising]

From Johannes: "Also, what would be very useful for the next section of the code-book (take your time of course, I'll just revisit it later) would be a "%likely" and "%unlikely" variables that hold all forms of the following constructs: "likelihood", "little likelihood", "unlikely", "apt to", "liable to", "chance of", "chance that", "chance for", "probability that", "will probably", "might", "may", "could", as well as variations. I actually think that the modal verb construct '%will' might present a problem, as it holds conceptually very different words."

Possibly don't use template syntax. Just %likely %event, or something like that.