Clarify how magic wand instances are matched with those in the current state

> Created by **@alexanderjsummers** on 2019-08-28 10:55

We should document this in the tutorial \(though it is a little advanced\): all expressions which don't depend on the "current" \(lhs/rhs\) heap are matched by value; those which do depend on the current heap are matched syntactically. We should add examples.
