Add binding forms, make macro tracing more robust

binding is a new hack which allows things like

(binding
  ...
  (bind x 1)
  (bind y 2)
  ...
  (bind (f a b)
    (+ a b))
  (f x y))

These get expanded into code which uses let* &c.

trace-macro is also a bit more robust against possible bad tracing states (for instance if it thinks it should be tracing but there's no wrapped hook it will offer ways to recover). None of these should ever happen in practice.

Initial public version

v1.0.0

v1.0.0