Drop count

- Supporting count is far more problematic than what the worth is.  If
  desired, count can be emulated using a capture.
Make capture evaluate in sub-expression context again

- In accordance with what's currently in dwgrep.txt.
Change ?{}, !{}, ?all{}, !all{} to ?(), !(), ?all(), !all()
Drop stack slot coodinate handling from tree.cc/tree.hh

- These are sure to come back in some form later, but right now we
  don't need them.
Drop CLOSE_PLUS and MAYBE tree types

- Translate X+ and X? directly to X X* and (X,).
Drop slot_idx.cc/.hh
Drop inaccurate part of a comment
Drop irrelevant part of a comment