message: Un-specify printing pointers (fix ##230)
  Just add a note to say that implementations can do whatever they want.
diff: @@ -40,3 +40,11 @@ These are the operations that manipulate memory allocations:
  It is an error to access or free a region that has already been freed.
  It is also an error to access (`load` or `store`) a pointer that is out of bounds, i.e., outside the range of valid indices for a given allocation.
  (Doing a `ptradd` to produce an out-of-bounds pointer is not an error; subsequently accessing that pointer is.)
  +
  +Printing
  +--------
  +
  +It is not an error to use the [core][] `print` operation on pointers, but the output is not specified.
  +Implementations can choose to print any representation of the pointer that they deem helpful.
  +
  +[core]: ./core.md
  