Updated the parser extension to reflect recent designs.
Made post-clone freeing overridable and altered constness in clone wrappers.  Also made annotation storage mutable (to save on const_casts), and added an annotation-canonicalizing member function.  Made justification and unjustification const to match.
Added the pipe character as whitespace (it being treated by ni as a paragraph break) and introduced a digit predicate.
Built buffer infrastructure for CYK filtering.
Built session infrastructure for CYK filtering.
Wrote CYK filtering, which is a lot fiddlier than I thought it would be, and involved some dancing around the fully-dynamic-reachability elephant in the room.  Currently this compiles, but almost certainly does the wrong thing---at the very least the contract for next_token has changed, but its implementation hasn't yet.